sql: disallow schema changes for READ COMMITTED transactions

pkg/sql/logictest/testdata/logic_test/select_for_update_read_committed → pkg/sql/logictest/testdata/logic_test/read_committed

@@ -1,5 +1,7 @@
 # LogicTest: !local-mixed-22.2-23.1
 
+subtest select_for_update
+
 # SELECT FOR UPDATE is prohibited under weaker isolation levels until we improve
 # locking. See #57031, #75457, #100144.
 
@@ -88,22 +90,27 @@ SELECT aisle + 1 FROM s
 statement ok
 ROLLBACK
 
-statement ok
-SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED
-
-# Creating a UDF using SELECT FOR UPDATE should succeed under read committed.
 statement ok
 CREATE FUNCTION wrangle (name STRING) RETURNS INT LANGUAGE SQL AS $$
   SELECT aisle FROM supermarket WHERE person = name FOR UPDATE
 $$
 
+statement ok
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED
+
 # But calling that function should fail.
 query error pgcode 0A000 cannot execute SELECT FOR UPDATE statements under ReadCommitted isolation
 INSERT INTO supermarket (person, aisle) VALUES ('grandma', wrangle('matilda'))
 
+statement ok
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SERIALIZABLE
+
 statement ok
 DROP FUNCTION wrangle
 
+statement ok
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED
+
 # Preparing a SELECT FOR UPDATE should succeed under read committed.
 statement ok
 PREPARE psa AS SELECT aisle FROM supermarket WHERE person = $1::STRING FOR UPDATE
@@ -138,5 +145,92 @@ SELECT aisle
   WHERE starts_with = 'm' AND ends_with = 'lda'
   FOR UPDATE
 
+subtest end
+
+subtest schema_changes
+
+# Schema changes are prohibited under weaker isolation levels.
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER TABLE supermarket ADD COLUMN age INT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE TABLE foo(a INT)
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+DROP TABLE supermarket
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE USER foo
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+DROP USER testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT admin TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT SELECT ON supermarket TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT USAGE ON SCHEMA public TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT CONNECT ON DATABASE postgres TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE INDEX foo ON supermarket(ends_with, starts_with)
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE FUNCTION f (x INT) RETURNS INT LANGUAGE SQL AS $$
+  SELECT x+1
+$$
+
+statement ok
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE FUNCTION f (x INT) RETURNS INT LANGUAGE SQL AS $$
+  SELECT x+1
+$$;
+COMMIT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER FUNCTION f (x INT) RENAME TO g
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT EXECUTE ON FUNCTION f (x INT) TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE TYPE typ AS ENUM('a', 'b')
+
+statement ok
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE TYPE typ AS ENUM('a', 'b');
+COMMIT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER TYPE typ ADD VALUE 'c'
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT USAGE ON TYPE typ TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE DATABASE foo
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER DATABASE postgres RENAME TO foo
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE SCHEMA s
+
+statement ok
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE SCHEMA s;
+COMMIT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER SCHEMA s RENAME TO foo
+
+subtest end
+
 statement ok
 SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SERIALIZABLE

pkg/sql/opt/exec/execbuilder/relational.go

@@ -168,6 +168,11 @@ func (b *Builder) buildRelational(e memo.RelExpr) (execPlan, error) {
 	var err error
 
 	if opt.IsDDLOp(e) {
+		if b.evalCtx.Txn.IsoLevel().ToleratesWriteSkew() {
+			return execPlan{}, pgerror.Newf(
+				pgcode.FeatureNotSupported, "transaction involving a schema change needs to be SERIALIZABLE",
+			)
+		}
 		// Mark the statement as containing DDL for use
 		// in the SQL executor.
 		b.IsDDL = true

pkg/sql/parser/sql.y

@@ -6818,7 +6818,7 @@ set_exprs_internal:
      It cannot be used by clients. */
   SET ROW '(' expr_list ')'
   {
-    $$.val = &tree.SetVar{Values: $4.exprs()}
+    $$.val = &tree.SetVar{Values: $4.exprs(), SetRow: true}
   }
 
 // %Help: SET SESSION - change a session variable

pkg/sql/parser/testdata/set

@@ -626,3 +626,11 @@ SET LOCAL tracing = 'off'
 SET LOCAL tracing = ('off') -- fully parenthesized
 SET LOCAL tracing = '_' -- literals removed
 SET LOCAL tracing = 'off' -- identifiers removed
+
+parse
+SET "" = 'a'
+----
+SET "" = 'a'
+SET "" = ('a') -- fully parenthesized
+SET "" = '_' -- literals removed
+SET "" = 'a' -- identifiers removed

pkg/sql/sem/tree/set.go

@@ -26,6 +26,7 @@ type SetVar struct {
 	Values   Exprs
 	Reset    bool
 	ResetAll bool
+	SetRow   bool
 }
 
 // Format implements the NodeFormatter interface.
@@ -47,7 +48,7 @@ func (node *SetVar) Format(ctx *FmtCtx) {
 	if node.Local {
 		ctx.WriteString("LOCAL ")
 	}
-	if node.Name == "" {
+	if node.SetRow {
 		ctx.WriteString("ROW (")
 		ctx.FormatNode(&node.Values)
 		ctx.WriteString(")")