Base information_schema.sql_identifier domain on name, not varchar.

tglsfdc · tglsfdc · commit 7c15cef86d37 · 2018-12-20T16:21:59.000-05:00
The SQL spec says that sql_identifier is a domain over varchar, but it also says that that domain is supposed to represent the set of valid identifiers for the implementation, in particular applying a length limit matching the implementation's identifier length limit. We were declaring sql_identifier as just "character varying", thus duplicating what the spec says about base type, but entirely failing at the rest of it. Instead, let's declare sql_identifier as a domain over type "name". (We can drop the COLLATE "C" added by commit 6b0faf7, since that's now implicit in "name".) With the recent improvements to name's comparison support, there's not a lot of functional difference between name and varchar. So although in principle this is a spec deviation, it's a pretty minor one. And correctly enforcing PG's name length limit is a good thing; on balance this seems closer to the intent of the spec than what we had. But that's all just language-lawyering. The *real* reason to do this is that it makes sql_identifier columns exposed by information_schema views be just direct representations of the underlying "name" catalog columns, eliminating a semantic mismatch that was disastrous for performance of typical queries on the information_schema. In combination with the recent change to allow dropping no-op CoerceToDomain nodes, this allows (for example) queries such as select ... from information_schema.tables where table_name = 'foo'; to produce an indexscan rather than a seqscan on pg_class. Discussion: https://postgr.es/m/CAFj8pRBUCX4LZ2rA2BbEkdD6NN59mgx+BLo1gO08Wod4RLtcTg@mail.gmail.com
diff --git a/src/backend/catalog/information_schema.sql b/src/backend/catalog/information_schema.sql
@@ -216,7 +216,7 @@ CREATE DOMAIN character_data AS character varying COLLATE "C";
  * SQL_IDENTIFIER domain
  */
 
-CREATE DOMAIN sql_identifier AS character varying COLLATE "C";
+CREATE DOMAIN sql_identifier AS name;
 
 
 /*
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201812201
+#define CATALOG_VERSION_NO	201812202
 
 #endif
