sql: restore invalid prepared statements in session migration

A schema change can make an existing prepared statement invalid. Rather
than returning an error when deserializing that invalid statement, now
the error will be returned only when trying to use the statement. This
makes a session migration even more transparent to the end user.

Release note: None

pkg/sql/conn_executor_prepare.go

@@ -203,6 +203,7 @@ func (ex *connExecutor) prepare(
 		prepared.PrepareMetadata = querycache.PrepareMetadata{
 			PlaceholderTypesInfo: tree.PlaceholderTypesInfo{
 				TypeHints: placeholderHints,
+				Types:     placeholderHints,
 			},
 		}
 		prepared.Statement = stmt.Statement
@@ -225,13 +226,13 @@ func (ex *connExecutor) prepare(
 
 	if txn := ex.state.mu.txn; txn != nil && txn.IsOpen() {
 		// Use the existing transaction.
-		if err := prepare(ctx, txn); err != nil {
+		if err := prepare(ctx, txn); err != nil && origin != PreparedStatementOriginSessionMigration {
 			return nil, err
 		}
 	} else {
 		// Use a new transaction. This will handle retriable errors here rather
 		// than bubbling them up to the connExecutor state machine.
-		if err := ex.server.cfg.DB.Txn(ctx, prepare); err != nil {
+		if err := ex.server.cfg.DB.Txn(ctx, prepare); err != nil && origin != PreparedStatementOriginSessionMigration {
 			return nil, err
 		}
 		// Prepare with an implicit transaction will end up creating

pkg/sql/testdata/session_migration/prepared_statements

@@ -17,6 +17,34 @@ wire_prepare s2
 INSERT INTO t VALUES($1, $2, $3)
 ----
 
+exec
+ALTER TABLE t RENAME TO t2
+----
+
+wire_prepare s3
+INSERT INTO t2 VALUES($1, $2, $3)
+----
+
+exec
+ALTER TABLE t2 DROP COLUMN c
+----
+
+wire_prepare s4
+INSERT INTO t2 VALUES($1, $2)
+----
+
+wire_exec s2 1 cat 2022-02-10
+----
+ERROR: relation "t" does not exist (SQLSTATE 42P01)
+
+wire_exec s3 1 cat 2022-02-10
+----
+ERROR: INSERT has more expressions than target columns, 3 expressions for 2 targets (SQLSTATE 42601)
+
+query
+SELECT * FROM t2
+----
+
 let $x
 SELECT encode(crdb_internal.serialize_session(), 'hex')
 ----
@@ -46,13 +74,23 @@ EXECUTE s1
 ----
 1
 
+# The s2 and s3 statements should experience the same errors that they did
+# before the session migration.
 wire_exec s2 1 cat 2022-02-10
 ----
+ERROR: relation "t" does not exist (SQLSTATE 42P01)
+
+wire_exec s3 1 cat 2022-02-10
+----
+ERROR: INSERT has more expressions than target columns, 3 expressions for 2 targets (SQLSTATE 42601)
+
+wire_exec s4 1 cat
+----
 
 query
-SELECT * FROM t
+SELECT * FROM t2
 ----
-1 cat 2022-02-10 00:00:00 +0000 UTC
+1 cat
 
 reset
 ----