sql: portable SHOW CREATE FUNCTION output

[bghal]

Previously, the SHOW CREATE FUNCTION statement would include the fully
qualified table names.

The database component of the table name made it unportable.

This change uses the unqualified table name to make the output portable.

Fixes: #125936
Epic: CRDB-39674

Release note (sql change): The SHOW CREATE FUNCTION statement produces
the 2-part table names rather than qualifying with the current database.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is 

[spilchen]

Looks great. I had some additional test suggestions.

Reviewed 11 of 11 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @jeffswenson)

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pkg/sql/show_create_clauses.go line 282 at r1 (raw file):

	// walking the table names using the reformat option. the buffer is simply discarded
	f := tree.NewFmtCtx(tree.FmtSimple, tree.FmtReformatTableNames(func(ctx *tree.FmtCtx, tn *tree.TableName) {

nit: we have two formatters in this function f and fmtCtx. It's subtle stuff to understand why two are needed. I suggest using better variable names. For example, f could be renamed to dbStripCtx and fmtCtx could be renamed to prettyPrintCtx

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pkg/sql/show_create_clauses.go line 283 at r1 (raw file):

	// walking the table names using the reformat option. the buffer is simply discarded
	f := tree.NewFmtCtx(tree.FmtSimple, tree.FmtReformatTableNames(func(ctx *tree.FmtCtx, tn *tree.TableName) {
		if string(tn.CatalogName) == databaseName {

nit: it's probably fine, but can we have a test where a database name has a unicode character and a case-sensitive name (e.g. "myDB")?

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pkg/sql/show_create_clauses.go line 294 at r1 (raw file):

	switch lang {
	case catpb.Function_SQL:
		parsedStmts, err := parser.Parse(queries)

The function bodies in triggers are lazily evaluated. So, you can have reference to non-existent objects. I think this should still parse fine, but could you ensure we have some SHOW CREATE FUNCTION tests for these?

For example, in both cases the objects referenced in the select don't exist. These are allowed to be created. And you will get a non-existent object when you try to use the function in a trigger:

create function t1() returns trigger as $$ BEGIN select not valid(); end; $$ LANGUAGE PLpgSQL;
create function t2() returns trigger as $$ BEGIN select 1 from a.b.c; end; $$ LANGUAGE PLpgSQL;

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pkg/sql/show_create_clauses.go line 327 at r1 (raw file):

		fmtCtx.FormatNode(stmts)
	default:
		return queries, nil

I think we only support SQL and PLpgSQL. Can we turn this into an assertion failure instead? That way if we add a new one in the future, we will know to update this code.

[bghal]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @jeffswenson and @spilchen)

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pkg/sql/show_create_clauses.go line 294 at r1 (raw file):

Previously, spilchen wrote…

The function bodies in triggers are lazily evaluated. So, you can have reference to non-existent objects. I think this should still parse fine, but could you ensure we have some SHOW CREATE FUNCTION tests for these?

For example, in both cases the objects referenced in the select don't exist. These are allowed to be created. And you will get a non-existent object when you try to use the function in a trigger:

create function t1() returns trigger as $$ BEGIN select not valid(); end; $$ LANGUAGE PLpgSQL;
create function t2() returns trigger as $$ BEGIN select 1 from a.b.c; end; $$ LANGUAGE PLpgSQL;

Done.

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pkg/sql/show_create_clauses.go line 327 at r1 (raw file):

Previously, spilchen wrote…

I think we only support SQL and PLpgSQL. Can we turn this into an assertion failure instead? That way if we add a new one in the future, we will know to update this code.

Changed it to an error return or what do you mean by an assertion failure here?

The other format helpers just return empty strings without error (1, 2.