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Document the system attributes ctid and tableoid, which for some reason

were never yet mentioned anywhere in our documentation. Improveexplanations of the other system attributes, too.

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doc/src/sgml
- syntax.sgml

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`‎doc/src/sgml/syntax.sgml`

Lines changed: 45 additions & 10 deletions

Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,5 @@`
`1`	`1`	`<!--`
`2`		`-$Header: /cvsroot/pgsql/doc/src/sgml/syntax.sgml,v 1.32 2001/01/06 11:58:56 petere Exp $`
	`2`	`+$Header: /cvsroot/pgsql/doc/src/sgml/syntax.sgml,v 1.33 2001/01/08 22:07:47 tgl Exp $`
`3`	`3`	`-->`
`4`	`4`
`5`	`5`	`<chapter id="sql-syntax">`
`@@ -568,27 +568,33 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )`
`568`	`568`	`<term>oid</term>`
`569`	`569`	`<listitem>`
`570`	`570`	`<para>`
`571`		`-stands for theunique identifier ofan instance whichisadded by`
`572`		`- Postgres to allinstances automatically. OIDs are not reused and are`
`573`		`- 32-bit quantities.`
	`571`	`+Theunique identifier(object ID)ofa row. Thisisa serial number`
	`572`	`+that is added byPostgres to allrows automatically. OIDs are not`
	`573`	`+reused and are32-bit quantities.`
`574`	`574`	`</para>`
`575`	`575`	`</listitem>`
`576`	`576`	`</varlistentry>`
`577`	`577`
`578`	`578`	`<varlistentry>`
`579`		`-<term>xmin</term>`
	`579`	`+ <term>tableoid</term>`
`580`	`580`	`<listitem>`
`581`	`581`	`<para>`
`582`		`- The identity of the inserting transaction.`
	`582`	`+ The OID of the table containing this row. This attribute is`
	`583`	`+ particularly handy for queries that select from inheritance`
	`584`	`+ hierarchies, since without it, it's difficult to tell which`
	`585`	`+ individual table a row came from. The tableoid can be joined`
	`586`	`+ against the OID attribute of pg_class to obtain the table name.`
`583`	`587`	`</para>`
`584`	`588`	`</listitem>`
`585`	`589`	`</varlistentry>`
`586`	`590`
`587`	`591`	`<varlistentry>`
`588`		`- <term>xmax</term>`
	`592`	`+<term>xmin</term>`
`589`	`593`	`<listitem>`
`590`	`594`	`<para>`
`591`		`- The identity of the deleting transaction.`
	`595`	`+ The identity (transaction ID) of the inserting transaction for`
	`596`	`+ this tuple. (Note: a tuple is an individual state of a row;`
	`597`	`+ each UPDATE of a row creates a new tuple for the same logical row.)`
`592`	`598`	`</para>`
`593`	`599`	`</listitem>`
`594`	`600`	`</varlistentry>`
`@@ -597,7 +603,19 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )`
`597`	`603`	`<term>cmin</term>`
`598`	`604`	`<listitem>`
`599`	`605`	`<para>`
`600`		`- The command identifier within the inserting transaction.`
	`606`	`+ The command identifier (starting at zero) within the inserting`
	`607`	`+ transaction.`
	`608`	`+</para>`
	`609`	`+ </listitem>`
	`610`	`+ </varlistentry>`
	`611`	`+`
	`612`	`+ <varlistentry>`
	`613`	`+ <term>xmax</term>`
	`614`	`+ <listitem>`
	`615`	`+<para>`
	`616`	`+ The identity (transaction ID) of the deleting transaction,`
	`617`	`+ or zero for an undeleted tuple. In practice, this is never nonzero`
	`618`	`+ for a visible tuple.`
`601`	`619`	`</para>`
`602`	`620`	`</listitem>`
`603`	`621`	`</varlistentry>`
`@@ -606,7 +624,24 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )`
`606`	`624`	`<term>cmax</term>`
`607`	`625`	`<listitem>`
`608`	`626`	`<para>`
`609`		`- The command identifier within the deleting transaction.`
	`627`	`+ The command identifier within the deleting transaction, or zero.`
	`628`	`+ Again, this is never nonzero for a visible tuple.`
	`629`	`+</para>`
	`630`	`+ </listitem>`
	`631`	`+ </varlistentry>`
	`632`	`+`
	`633`	`+ <varlistentry>`
	`634`	`+ <term>ctid</term>`
	`635`	`+ <listitem>`
	`636`	`+<para>`
	`637`	`+ The tuple ID of the tuple within its table. This is a pair`
	`638`	`+ (block number, tuple index within block) that identifies the`
	`639`	`+ physical location of the tuple. Note that although the ctid`
	`640`	`+ can be used to locate the tuple very quickly, a row's ctid`
	`641`	`+ will change each time it is updated or moved by VACUUM.`
	`642`	`+ Therefore ctid is useless as a long-term row identifier.`
	`643`	`+ The OID, or even better a user-defined serial number, should`
	`644`	`+ be used to identify logical rows.`
`610`	`645`	`</para>`
`611`	`646`	`</listitem>`
`612`	`647`	`</varlistentry>`

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