add --skip-strict-mode option

doc/command-line-flags.md

@@ -173,6 +173,10 @@ See also: [`concurrent-migrations`](cheatsheet.md#concurrent-migrations) on the
 
 By default `gh-ost` verifies no foreign keys exist on the migrated table. On servers with large number of tables this check can take a long time. If you're absolutely certain no foreign keys exist (table does not reference other table nor is referenced by other tables) and wish to save the check time, provide with `--skip-foreign-key-checks`.
 
+### skip-strict-mode
+
+By default `gh-ost` enforces STRICT_ALL_TABLES sql_mode as a safety measure. In some cases this changes the behaviour of other modes (namely ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE) which may lead to errors during migration. Use `--skip-strict-mode` to explicitly tell `gh-ost` not to enforce this. **Danger** This may have some unexpected disastrous side effects.
+
 ### skip-renamed-columns
 
 See [`approve-renamed-columns`](#approve-renamed-columns)

go/base/context.go

@@ -86,6 +86,7 @@ type MigrationContext struct {
 	SwitchToRowBinlogFormat  bool
 	AssumeRBR                bool
 	SkipForeignKeyChecks     bool
+	SkipStrictMode           bool
 	NullableUniqueKeyAllowed bool
 	ApproveRenamedColumns    bool
 	SkipRenamedColumns       bool

go/cmd/gh-ost/main.go

@@ -72,6 +72,7 @@ func main() {
 	flag.BoolVar(&migrationContext.IsTungsten, "tungsten", false, "explicitly let gh-ost know that you are running on a tungsten-replication based topology (you are likely to also provide --assume-master-host)")
 	flag.BoolVar(&migrationContext.DiscardForeignKeys, "discard-foreign-keys", false, "DANGER! This flag will migrate a table that has foreign keys and will NOT create foreign keys on the ghost table, thus your altered table will have NO foreign keys. This is useful for intentional dropping of foreign keys")
 	flag.BoolVar(&migrationContext.SkipForeignKeyChecks, "skip-foreign-key-checks", false, "set to 'true' when you know for certain there are no foreign keys on your table, and wish to skip the time it takes for gh-ost to verify that")
+	flag.BoolVar(&migrationContext.SkipStrictMode, "skip-strict-mode", false, "explicitly tell gh-ost binlog applier not to enforce strict sql mode")
 	flag.BoolVar(&migrationContext.AliyunRDS, "aliyun-rds", false, "set to 'true' when you execute on Aliyun RDS.")
 	flag.BoolVar(&migrationContext.GoogleCloudPlatform, "gcp", false, "set to 'true' when you execute on a 1st generation Google Cloud Platform (GCP).")
 

go/logic/applier.go

@@ -482,10 +482,10 @@ func (this *Applier) ApplyIterationInsertQuery() (chunkSize int64, rowsAffected
 			return nil, err
 		}
 		defer tx.Rollback()
-		sessionQuery := fmt.Sprintf(`SET
-			SESSION time_zone = '%s',
-			sql_mode = CONCAT(@@session.sql_mode, ',STRICT_ALL_TABLES')
-			`, this.migrationContext.ApplierTimeZone)
+		sessionQuery := fmt.Sprintf(`SET SESSION time_zone = '%s'`, this.migrationContext.ApplierTimeZone)
+		if !this.migrationContext.SkipStrictMode {
+			sessionQuery += ", sql_mode = CONCAT(@@session.sql_mode, ',STRICT_ALL_TABLES')"
+		}
 		if _, err := tx.Exec(sessionQuery); err != nil {
 			return nil, err
 		}
@@ -1005,10 +1005,10 @@ func (this *Applier) ApplyDMLEventQuery(dmlEvent *binlog.BinlogDMLEvent) error {
 				tx.Rollback()
 				return err
 			}
-			sessionQuery := `SET
-			SESSION time_zone = '+00:00',
-			sql_mode = CONCAT(@@session.sql_mode, ',STRICT_ALL_TABLES')
-			`
+			sessionQuery := fmt.Sprintf("SET SESSION time_zone = '+00:00'")
+			if !this.migrationContext.SkipStrictMode {
+				sessionQuery += ", sql_mode = CONCAT(@@session.sql_mode, ',STRICT_ALL_TABLES')"
+			}
 			if _, err := tx.Exec(sessionQuery); err != nil {
 				return rollback(err)
 			}
@@ -1050,10 +1050,10 @@ func (this *Applier) ApplyDMLEventQueries(dmlEvents [](*binlog.BinlogDMLEvent))
 			return err
 		}
 
-		sessionQuery := `SET
-			SESSION time_zone = '+00:00',
-			sql_mode = CONCAT(@@session.sql_mode, ',STRICT_ALL_TABLES')
-			`
+		sessionQuery := "SET SESSION time_zone = '+00:00'"
+		if !this.migrationContext.SkipStrictMode {
+			sessionQuery += ", sql_mode = CONCAT(@@session.sql_mode, ',STRICT_ALL_TABLES')"
+		}
 		if _, err := tx.Exec(sessionQuery); err != nil {
 			return rollback(err)
 		}