fix GetConstraints for MySQL 5.7

MySQL 5.7 doesn't support SELECT ... WHERE ... without a FROM clause, which
causes the introspection_scripts/mysql_constraints.sql script to fail.

Fixed by adding a FROM information_schema.table_constraints to the first part
of the query.

ddl/START_HERE.md

@@ -78,6 +78,7 @@ If you have docker, you can use the docker-compose.yml (run `docker-compose up`)
 # docker-compose up -d
 POSTGRES_URL='postgres://user1:Hunter2!@localhost:5456/sakila?sslmode=disable'
 MYSQL_URL='root:Hunter2!@tcp(localhost:3330)/sakila?multiStatements=true&parseTime=true'
+MYSQL5_URL='root:Hunter2!@tcp(localhost:3320)/sakila?multiStatements=true&parseTime=true'
 MARIADB_URL='root:Hunter2!@tcp(localhost:3340)/sakila?multiStatements=true&parseTime=true'
 SQLSERVER_URL='sqlserver://sa:Hunter2!@localhost:1447'
 ```

ddl/integration_test.go

@@ -84,6 +84,7 @@ func TestMySQL(t *testing.T) {
 	if err != nil {
 		t.Fatal(testutil.Callers(), err)
 	}
+
 	dbi := NewDatabaseIntrospector(dialect, db)
 	version, err := dbi.GetVersion()
 	if err != nil {
@@ -92,6 +93,15 @@ func TestMySQL(t *testing.T) {
 	if strings.Contains(version, "MariaDB") {
 		t.Skip("skipping integration tests for MariaDB because it doesn't support indexed expressions (which are present in the mysql migration scripts)")
 	}
+
+	versionNums, err := dbi.GetVersionNums()
+	if err != nil {
+		t.Fatal(testutil.Callers(), err)
+	}
+	if versionNums.LowerThan(8) {
+		t.Skip(fmt.Sprintf("skipping integration tests for MySQL %d because the tests are only designed for MySQL 8 and above", versionNums[0]))
+	}
+
 	t.Parallel()
 	testMigrateIntrospect(t, dialect, driver, *mysqlDSN)
 	testAutomigrate(t, dialect, *mysqlDSN,

ddl/introspection_scripts/mysql_constraints.sql

@@ -11,6 +11,8 @@ SELECT
     ,'' AS delete_rule
     ,'' AS match_option
     ,'' AS check_expr
+FROM
+    information_schema.table_constraints
 WHERE
     FALSE
 {{- if .IncludeConstraintType "PRIMARY KEY" }}

docker-compose.yml

@@ -27,6 +27,20 @@ services:
       MYSQL_DATABASE: 'sakila'
     platform: 'linux/amd64'
 
+  mysql5:
+    container_name: 'mysql5_sakila'
+    image: 'mysql:5.7'
+    ports:
+      - '3320:3306'
+    volumes:
+      - 'mysql5_data:/var/lib/mysql'
+    environment:
+      MYSQL_ROOT_PASSWORD: 'Hunter2!'
+      MYSQL_USER: 'user1'
+      MYSQL_PASSWORD: 'Hunter2!'
+      MYSQL_DATABASE: 'sakila'
+    platform: 'linux/amd64'
+
   mariadb:
     container_name: 'mariadb_sakila'
     image: 'mariadb'
@@ -70,6 +84,7 @@ services:
 volumes:
   postgres_data:
   mysql_data:
+  mysql5_data:
   mariadb_data:
   sqlserver_data:
   # oracle_data: