Drop existing default on Users.Timezone prior to column type change (#18669)

store/sqlstore/store.go

@@ -133,6 +133,7 @@ type SqlStore struct {
 // ColumnInfo holds information about a column.
 type ColumnInfo struct {
 	DataType          string
+	DefaultValue      string
 	CharMaximumLength int
 }
 
@@ -651,7 +652,7 @@ func (ss *SqlStore) GetColumnInfo(tableName, columnName string) (*ColumnInfo, er
 	var columnInfo ColumnInfo
 	if ss.DriverName() == model.DatabaseDriverPostgres {
 		err := ss.GetMaster().SelectOne(&columnInfo,
-			`SELECT data_type as DataType,
+			`SELECT data_type as DataType, COALESCE(column_default, '') as DefaultValue,
 					COALESCE(character_maximum_length, 0) as CharMaximumLength
 			 FROM information_schema.columns
 			 WHERE lower(table_name) = lower($1)
@@ -663,7 +664,7 @@ func (ss *SqlStore) GetColumnInfo(tableName, columnName string) (*ColumnInfo, er
 		return &columnInfo, nil
 	} else if ss.DriverName() == model.DatabaseDriverMysql {
 		err := ss.GetMaster().SelectOne(&columnInfo,
-			`SELECT data_type as DataType,
+			`SELECT data_type as DataType, COALESCE(column_default, '') as DefaultValue,
 					COALESCE(character_maximum_length, 0) as CharMaximumLength
 			 FROM information_schema.columns
 			 WHERE table_schema = DATABASE()