output.
indicates that the query should be run over only the
<classname>cities</classname> table, and not tables below
<classname>cities</classname> in the inheritance hierarchy. Many
- of the commands that we have already discussed --
+ of the commands that we have already discussed —
<command>SELECT</command>, <command>UPDATE</command>, and
- <command>DELETE</command> -- support this <literal>ONLY</literal>
+ <command>DELETE</command> — support this <literal>ONLY</literal>
notation.
</para>
</programlisting>
However, the current implementation does not enforce the array size
- limits --- the behavior is the same as for arrays of unspecified
+ limits — the behavior is the same as for arrays of unspecified
length.
</para>
the administrator specify a shell command to be executed to copy a
completed segment file to wherever it needs to go. The command could be
as simple as a <application>cp</>, or it could invoke a complex shell
- script --- it's all up to you.
+ script — it's all up to you.
</para>
<para>
last base backup, the interval between base backups should usually be
chosen based on how much storage you want to expend on archived WAL
files. You should also consider how long you are prepared to spend
- recovering, if recovery should be necessary --- the system will have to
+ recovering, if recovery should be necessary — the system will have to
replay all those WAL segments, and that could take awhile if it has
been a long time since the last base backup.
</para>
Normally, one should not change the system catalogs by hand, there
are always SQL commands to do that. (For example, <command>CREATE
DATABASE</command> inserts a row into the
- <structname>pg_database</structname> catalog --- and actually
+ <structname>pg_database</structname> catalog — and actually
creates the database on disk.) There are some exceptions for
particularly esoteric operations, such as adding index access methods.
</para>
not in its <structname>pg_opclass</structname> row, but in the associated
rows in <structname>pg_amop</structname> and
<structname>pg_amproc</structname>. Those rows are considered to be
- part of the operator class definition --- this is not unlike the way
+ part of the operator class definition — this is not unlike the way
that a relation is defined by a single <structname>pg_class</structname>
row plus associated rows in <structname>pg_attribute</structname> and
other tables.
<para>
<structname>pg_stats</structname> is also designed to present the
information in a more readable format than the underlying catalog
- --- at the cost that its schema must be extended whenever new slot types
+ — at the cost that its schema must be extended whenever new slot types
are defined for <structname>pg_statistic</structname>.
</para>
</para>
<para>
- If the conversion of a particular character is not possible --
- suppose you chose <literal>EUC_JP</literal> for the server and
- <literal>LATIN1</literal> for the client, then some Japanese
- characters cannot be converted to <literal>LATIN1</literal> -- it
- is transformed to its hexadecimal byte values in parentheses,
- e.g., <literal>(826C)</literal>.
+ If the conversion of a particular character is not possible
+ — suppose you chose <literal>EUC_JP</literal> for the
+ server and <literal>LATIN1</literal> for the client, then some
+ Japanese characters cannot be converted to
+ <literal>LATIN1</literal> — it is transformed to its
+ hexadecimal byte values in parentheses, e.g.,
+ <literal>(826C)</literal>.
</para>
</sect2>
specifies which <productname>PostgreSQL</productname> user name it
wants to connect as, much the same way one logs into a Unix computer
as a particular user. Within the SQL environment the active database
- user name determines access privileges to database objects -- see
+ user name determines access privileges to database objects — see
<xref linkend="user-manag"> for more information. Therefore, it is
essential to restrict which database users can connect.
</para>
<xref linkend="datetime-timezone-input-table"> shows the time zone
abbreviations recognized by <productname>PostgreSQL</productname>
in date/time input values. Note that these names are <emphasis>not</>
- used for date/time output --- display is driven by the currently
+ used for date/time output — display is driven by the currently
selected <xref linkend="guc-timezone"> parameter setting. (It is
likely that future releases will make some use of <varname>timezone</>
for input as well.)
identifiers are also 32-bit quantities. This creates a hard limit
of 2<superscript>32</> (4 billion) <acronym>SQL</acronym> commands
within a single transaction. In practice this limit is not a
- problem --- note that the limit is on number of
+ problem — note that the limit is on number of
<acronym>SQL</acronym> commands, not number of rows processed.
</para>
</sect1>
in memory when they are loaded by the executable. (Object files
intended for executables are usually not compiled that way.) The
command to link a shared library contains special flags to
- distinguish it from linking an executable. --- At least this is the
- theory. On some systems the practice is much uglier.
+ distinguish it from linking an executable (at least in theory
+ — on some systems the practice is much uglier).
</para>
<para>
This is the definition of DocBook itself. We currently use
version 4.2; you cannot use later or earlier versions. Note
that there is also an <acronym>XML</acronym> version of DocBook
- -- do not use that.
+ — do not use that.
</para>
</listitem>
</varlistentry>
<row>
<entry>Class 02</entry>
-<entry>No Data --- this is also a warning class per SQL99</entry>
+<entry>No Data — this is also a warning class per SQL99</entry>
</row>
<row>
if it is a member of the regular set described by the regular
expression. As with <function>LIKE</function>, pattern characters
match string characters exactly unless they are special characters
- in the regular expression language --- but regular expressions use
+ in the regular expression language — but regular expressions use
different special characters than <function>LIKE</function> does.
Unlike <function>LIKE</function> patterns, a
regular expression is allowed to match anywhere within a string, unless
SELECT pg_type_is_visible('myschema.widget'::regtype);
</programlisting>
Note that it would not make much sense to test an unqualified name in
- this way --- if the name can be recognized at all, it must be visible.
+ this way — if the name can be recognized at all, it must be visible.
</para>
<indexterm zone="functions-info">
The information schema consists of a set of views that contain
information about the objects defined in the current database. The
information schema is defined in the SQL standard and can therefore
- be expected to be portable and remain stable --- unlike the system
+ be expected to be portable and remain stable — unlike the system
catalogs, which are specific to
<productname>PostgreSQL</productname> and are modelled after
implementation concerns. The information schema views do not,
<listitem>
<para>
Converts an escaped string representation of binary data into binary
- data --- the reverse of <function>PQescapeBytea</function>.
+ data — the reverse of <function>PQescapeBytea</function>.
This is needed when retrieving <type>bytea</type> data in text format,
but not when retrieving it in binary format.
may be useful to set up periodic <application>cron</> tasks that
<command>VACUUM</command> only selected tables, skipping tables that are known not to
change often. This is only likely to be helpful if you have both
- large heavily-updated tables and large seldom-updated tables --- the
+ large heavily-updated tables and large seldom-updated tables — the
extra cost of vacuuming a small table isn't enough to be worth
worrying about.
</para>
The standard form of <command>VACUUM</> is best used with the goal
of maintaining a fairly level steady-state usage of disk space. If
you need to return disk space to the operating system you can use
- <command>VACUUM FULL</> --- but what's the point of releasing disk
+ <command>VACUUM FULL</> — but what's the point of releasing disk
space that will only have to be allocated again soon? Moderately
frequent standard <command>VACUUM</> runs are a better approach
than infrequent <command>VACUUM FULL</> runs for maintaining
(32 bits at this writing) a cluster that runs for a long time (more
than 4 billion transactions) will suffer <firstterm>transaction ID
wraparound</>: the XID counter wraps around to zero, and all of a sudden
- transactions that were in the past appear to be in the future --- which
+ transactions that were in the past appear to be in the future — which
means their outputs become invisible. In short, catastrophic data loss.
(Actually the data is still there, but that's cold comfort if you can't
get at it.)
is exactly one billion transactions: if you wait longer, it's possible
that a row version that was not quite old enough to be reassigned last time
is now more than two billion transactions old and has wrapped around
- into the future --- i.e., is lost to you. (Of course, it'll reappear
+ into the future — i.e., is lost to you. (Of course, it'll reappear
after another two billion transactions, but that's no help.)
</para>
The intuitive meaning (and mathematical definition) of
<quote>serializable</> execution is that any two successfully committed
concurrent transactions will appear to have executed strictly serially,
- one after the other --- although which one appeared to occur first may
+ one after the other — although which one appeared to occur first may
not be predictable in advance. It is important to realize that forbidding
the undesirable behaviors listed in <xref linkend="mvcc-isolevel-table">
is not sufficient to guarantee true serializability, and in fact
even if the name contains the word
<quote>row</quote>; the names of the lock modes are historical.
To some extent the names reflect the typical usage of each lock
- mode --- but the semantics are all the same. The only real difference
+ mode — but the semantics are all the same. The only real difference
between one lock mode and another is the set of lock modes with
which each conflicts. Two transactions cannot hold locks of conflicting
modes on the same table at the same time. (However, a transaction
of transactions not counted by the first. Doing the two sums in a
single serializable transaction will give an accurate picture of the
effects of transactions that committed before the serializable transaction
- started --- but one might legitimately wonder whether the answer is still
+ started — but one might legitimately wonder whether the answer is still
relevant by the time it is delivered. If the serializable transaction
itself applied some changes before trying to make the consistency check,
the usefulness of the check becomes even more debatable, since now it
<para>
<productname>PostgreSQL</>
programs (server and client) can issue their messages in
- your favorite language -- if the messages have been translated.
+ your favorite language — if the messages have been translated.
Creating and maintaining translated message sets needs the help of
people who speak their own language well and want to contribute to
the <productname>PostgreSQL</> effort. You do not have to be a
<title>Requirements</title>
<para>
- We won't judge your language skills -- this section is about
+ We won't judge your language skills — this section is about
software tools. Theoretically, you only need a text editor. But
this is only in the unlikely event that you do not want to try out
your translated messages. When you configure your source tree, be
<listitem>
<para>
- List of provided translations -- empty in the beginning.
+ List of provided translations — initially empty.
</para>
</listitem>
</varlistentry>
both for reducing planning time and for directing the planner to a
good query plan. If the planner chooses a bad join order by default,
you can force it to choose a better order via <literal>JOIN</> syntax
- --- assuming that you know of a better order, that is. Experimentation
+ — assuming that you know of a better order, that is. Experimentation
is recommended.
</para>
a parameter as the name of a table or column in an SQL command. To get
around this restriction, you can construct dynamic commands using
the <application>PL/pgSQL</application> <command>EXECUTE</command>
- statement --- at the price of constructing a new execution plan on
+ statement — at the price of constructing a new execution plan on
every execution.
</para>
control. <application>PL/pgSQL</>'s <command>BEGIN</>/<command>END</>
are only for grouping; they do not start or end a transaction.
Functions and trigger procedures are always executed within a transaction
- established by an outer query --- they cannot start or commit that
+ established by an outer query — they cannot start or commit that
transaction, since there would be no context for them to execute in.
However, a block containing an <literal>EXCEPTION</> clause effectively
forms a subtransaction that can be rolled back without affecting the
<command>CREATE FUNCTION</> command, declaring it as a function with
no arguments and a return type of <type>trigger</type>. Note that
the function must be declared with no arguments even if it expects
- to receive arguments specified in <command>CREATE TRIGGER</> ---
+ to receive arguments specified in <command>CREATE TRIGGER</> —
trigger arguments are passed via <varname>TG_ARGV</>, as described
below.
</para>
ErrorResponse, then reads and discards messages until a Sync is reached,
then issues ReadyForQuery and returns to normal message processing.
(But note that no skipping occurs if an error is detected
- <emphasis>while</> processing Sync --- this ensures that there is one
+ <emphasis>while</> processing Sync — this ensures that there is one
and only one ReadyForQuery sent for each Sync.)
</para>
value changes for any of the parameters the backend believes the
frontend should know about. Most commonly this occurs in response
to a <command>SET</> SQL command executed by the frontend, and
- this case is effectively synchronous --- but it is also possible
+ this case is effectively synchronous — but it is also possible
for parameter status changes to occur because the administrator
changed a configuration file and then sent the
<systemitem>SIGHUP</systemitem> signal to the postmaster. Also,
</para>
<Para>
- The cancellation signal may or may not have any effect --- for
+ The cancellation signal may or may not have any effect — for
example, if it arrives after the backend has finished processing
the query, then it will have no effect. If the cancellation is
effective, it results in the current command being terminated
not only that table but all of its subtable successors, unless the
key word <literal>ONLY</> precedes the table name. However, the
reference produces only the columns that appear in the named table
- --- any columns added in subtables are ignored.
+ — any columns added in subtables are ignored.
</para>
<sect3 id="queries-join">
<para>
The alias becomes the new name of the table reference for the
- current query -- it is no longer possible to refer to the table
+ current query — it is no longer possible to refer to the table
by the original name. Thus
<programlisting>
SELECT * FROM my_table AS m WHERE my_table.a > 5;
</screen>
This creates the scripts and compiles the C files containing user-defined
- functions and types. (You must use GNU make for this --- it may be named
+ functions and types. (You must use GNU make for this — it may be named
something different on your system, often <application>gmake</>.)
Then, to start the tutorial, do the following:
a type for storing single precision floating-point numbers.
<type>date</type> should be self-explanatory. (Yes, the column of
type <type>date</type> is also named <literal>date</literal>.
- This may be convenient or confusing -- you choose.)
+ This may be convenient or confusing — you choose.)
</para>
<para>
to rename <replaceable class="parameter">newtable</replaceable> to the old name, and
recreate the table's indexes. However, this approach does not preserve
OIDs, constraints, foreign key relationships, granted privileges, and
- other ancillary properties of the table --- all such items must be
+ other ancillary properties of the table — all such items must be
manually recreated.
</para>
</refsect1>
<term>Signature</term>
<listitem>
<para>
-11-byte sequence <literal>PGCOPY\n\377\r\n\0</> --- note that the zero byte
+11-byte sequence <literal>PGCOPY\n\377\r\n\0</> — note that the zero byte
is a required part of the signature. (The signature is designed to allow
easy identification of files that have been munged by a non-8-bit-clean
transfer. This signature will be changed by end-of-line-translation
<para>
If OIDs are included in the file, the OID field immediately follows the
field-count word. It is a normal field except that it's not included
-in the field-count. In particular it has a length word --- this will allow
+in the field-count. In particular it has a length word — this will allow
handling of 4-byte vs. 8-byte OIDs without too much pain, and will allow
OIDs to be shown as null if that ever proves desirable.
</para>
specifies whether data is to be retrieved in text or binary format.
This choice overrides the way that the cursor is defined. The concept
of a binary cursor as such is thus obsolete when using extended query
- protocol --- any cursor can be treated as either text or binary.
+ protocol — any cursor can be treated as either text or binary.
</para>
</note>
</refsect1>
TABLE</> statement before executing any data modification
statement. A serializable transaction's view of data will be
frozen when its first data modification statement begins. A later
- <command>LOCK TABLE</> will still prevent concurrent writes --- but it
+ <command>LOCK TABLE</> will still prevent concurrent writes — but it
won't ensure that what the transaction reads corresponds to the
latest committed values.
</para>
mode, and then be unable to also acquire <literal>ROW EXCLUSIVE</>
mode to actually perform their updates. (Note that a transaction's
own locks never conflict, so a transaction can acquire <literal>ROW
- EXCLUSIVE</> mode when it holds <literal>SHARE</> mode --- but not
+ EXCLUSIVE</> mode when it holds <literal>SHARE</> mode — but not
if anyone else holds <literal>SHARE</> mode.) To avoid deadlocks,
make sure all transactions acquire locks on the same objects in the
same order, and if multiple lock modes are involved for a single
<literal>SIGQUIT</literal> to terminate without the normal cleanup.
These signals <emphasis>should not</emphasis> be used by users. It is also
unwise to send <literal>SIGKILL</literal> to a <command>postgres</command>
- process --- the <command>postmaster</command> will interpret this as
+ process — the <command>postmaster</command> will interpret this as
a crash in <command>postgres</command>, and will force all the sibling
<command>postgres</command> processes to quit as part of its standard
crash-recovery procedure.
fail if you run the test on the day of a daylight-saving time
changeover, or the day after one. These queries expect that
the intervals between midnight yesterday, midnight today and
- midnight tomorrow are exactly twenty-four hours --- which is wrong
+ midnight tomorrow are exactly twenty-four hours — which is wrong
if daylight-saving time went into or out of effect meanwhile.
</para>
the remaining range-table entries in the top query (in this example there
are no more), and it will recursively check the range-table entries in
the added subquery to see if any of them reference views. (But it
- won't expand <literal>*OLD*</> or <literal>*NEW*</> --- otherwise we'd have infinite recursion!)
+ won't expand <literal>*OLD*</> or <literal>*NEW*</> — otherwise we'd have infinite recursion!)
In this example, there are no rewrite rules for <literal>shoelace_data</> or <literal>unit</>,
so rewriting is complete and the above is the final result given to
the planner.
error). The <function>errcode</> call specifies the SQLSTATE error code
using a macro defined in <filename>src/include/utils/errcodes.h</>. The
<function>errmsg</> call provides the primary message text. Notice the
- extra set of parentheses surrounding the auxiliary function calls ---
+ extra set of parentheses surrounding the auxiliary function calls —
these are annoying but syntactically necessary.
</para>
<para>
<acronym>SQL</acronym> allows one to partition the tuples of a table
into groups. Then the
- aggregate operators described above can be applied to the groups ---
+ aggregate operators described above can be applied to the groups —
i.e. the value of the aggregate operator is no longer calculated over
all the values of the specified column but over all values of a
group. Thus the aggregate operator is evaluated separately for every
<programlisting>
SELECT 5 ! (- 6);
</programlisting>
- because the parser has no idea -- until it is too late -- that
- <token>!</token> is defined as a postfix operator, not an infix one.
- To get the desired behavior in this case, you must write
+ because the parser has no idea — until it is too late
+ — that <token>!</token> is defined as a postfix operator,
+ not an infix one. To get the desired behavior in this case, you
+ must write
<programlisting>
SELECT (5 !) - 6;
</programlisting>
The first form of aggregate expression invokes the aggregate
across all input rows for which the given expression yields a
non-null value. (Actually, it is up to the aggregate function
- whether to ignore null values or not --- but all the standard ones do.)
+ whether to ignore null values or not — but all the standard ones do.)
The second form is the same as the first, since
<literal>ALL</literal> is the default. The third form invokes the
aggregate for all distinct non-null values of the expression found
<para>
By default, the value created by a <literal>ROW</> expression is of
an anonymous record type. If necessary, it can be cast to a named
- composite type --- either the rowtype of a table, or a composite type
+ composite type — either the rowtype of a table, or a composite type
created with <command>CREATE TYPE AS</>. An explicit cast may be needed
to avoid ambiguity. For example:
<programlisting>
we simply install a prior physical backup of the database, and
replay the WAL log just as far as the desired time. What's more,
the physical backup doesn't have to be an instantaneous snapshot
- of the database state --- if it is made over some period of time,
+ of the database state — if it is made over some period of time,
then replaying the WAL log for that period will fix any internal
inconsistencies.
</para>
<para>
To deal with the case where <filename>pg_control</filename> is
corrupted, we should support the possibility of scanning existing log
- segments in reverse order -- newest to oldest -- in order to find the
+ segments in reverse order — newest to oldest — in order to find the
latest checkpoint. This has not been implemented yet.
<filename>pg_control</filename> is small enough (less than one disk page)
that it is not subject to partial-write problems, and as of this writing
<para>
The above definition of <function>sum</function> will return zero (the initial
state condition) if there are no nonnull input values.
- Perhaps we want to return null in that case instead --- the SQL standard
+ Perhaps we want to return null in that case instead — the SQL standard
expects <function>sum</function> to behave that way. We can do this simply by
omitting the <literal>initcond</literal> phrase, so that the initial state
condition is null. Ordinarily this would mean that the <literal>sfunc</literal>
compiled into dynamically loadable objects (also called shared
libraries) and are loaded by the server on demand. The dynamic
loading feature is what distinguishes <quote>C language</> functions
- from <quote>internal</> functions --- the actual coding conventions
+ from <quote>internal</> functions — the actual coding conventions
are essentially the same for both. (Hence, the standard internal
function library is a rich source of coding examples for user-defined
C functions.)
<title>Calling Conventions Version 0 for C-Language Functions</title>
<para>
- We present the <quote>old style</quote> calling convention first --- although
+ We present the <quote>old style</quote> calling convention first — although
this approach is now deprecated, it's easier to get a handle on
initially. In the version-0 method, the arguments and result
of the C function are just declared in normal C style, but being
</programlisting>
if you plan to work with C strings. If you are writing a function
returning set, you can save the results of these functions in the
- <structname>FuncCallContext</> structure --- use the
+ <structname>FuncCallContext</> structure — use the
<structfield>tuple_desc</> or <structfield>attinmeta</> field
respectively.
</para>
<productname>PostgreSQL</productname>, but all index methods are
described in <classname>pg_am</classname>. It is possible to add a
new index method by defining the required interface routines and
- then creating a row in <classname>pg_am</classname> --- but that is
+ then creating a row in <classname>pg_am</classname> — but that is
far beyond the scope of this chapter.
</para>
Consider again the situation where we are storing in the index only
the bounding box of a complex object such as a polygon. In this
case there's not much value in storing the whole polygon in the index
- entry --- we may as well store just a simpler object of type
+ entry — we may as well store just a simpler object of type
<type>box</>. This situation is expressed by the <literal>STORAGE</>
option in <command>CREATE OPERATOR CLASS</>: we'd write something like
<literal>tab2.y = tab1.x</>, because the index-scan machinery expects
to see the indexed column on the left of the operator it is given.
<ProductName>PostgreSQL</ProductName> will <emphasis>not</> simply
- assume that this is a valid transformation --- the creator of the
+ assume that this is a valid transformation — the creator of the
<literal>=</> operator must specify that it is valid, by marking the
operator with commutator information.
</para>
projects / users / bernd / postgres.git / commitdiff