bigquery: does not support sync column default value (#95)

* bigquery: does not support sync column default value

* update doc

docs/bigquery.md

@@ -24,7 +24,7 @@ To replicate snapshot and incremental data of a TiDB Table to BigQuery:
 
 All DDL which will change the schema of table are supported (except index related), including:
 
-- Add column
+- Add column without default value
 - Drop column
 - Rename column
 - Drop table
@@ -34,3 +34,4 @@ All DDL which will change the schema of table are supported (except index relate
 >
 > 1. BigQuery has some limitations on modifying table schemas, like BigQuery does not support add a REQUIRED column to an existing table schema, refer to [BigQuery Docs](https://cloud.google.com/bigquery/docs/managing-table-schemas), in some cases, its better to recreate the table.
 > 2. The type mapping from TiDB to BigQuery is defined [here](https://github.com/pingcap-inc/tidb2dw/blob/main/pkg/bigquerysql/types.go).
+> 3. tidb2dw will not sync column's default value to BigQuery, when you add a new column with default value, it will throw an error, you'd better to recreate the table in BigQuery and start a new replication task.

pkg/bigquerysql/ddl.go

@@ -2,7 +2,6 @@ package bigquerysql
 
 import (
 	"fmt"
-	"strconv"
 	"strings"
 
 	"github.com/pingcap-inc/tidb2dw/pkg/tidbsql"
@@ -23,13 +22,6 @@ func GetColumnModifyString(diff *tidbsql.ColumnDiff) (string, error) {
 		// https://cloud.google.com/bigquery/docs/reference/standard-sql/conversion_rules
 		strs = append(strs, fmt.Sprintf("`%s` SET DATA TYPE %s", diff.After.Name, colType))
 	}
-	if diff.Before.Default != diff.After.Default {
-		if diff.After.Default == nil {
-			strs = append(strs, fmt.Sprintf("`%s` DROP DEFAULT", diff.After.Name))
-		} else {
-			strs = append(strs, fmt.Sprintf("`%s` SET DEFAULT %s", diff.After.Name, getDefaultString(diff.After.Default)))
-		}
-	}
 	if diff.Before.Nullable != diff.After.Nullable {
 		if diff.After.Nullable == "true" {
 			strs = append(strs, fmt.Sprintf("`%s` DROP NOT NULL", diff.After.Name))
@@ -80,12 +72,7 @@ func GenDDLViaColumnsDiff(datasetID, tableID string, prevColumns []cloudstorage.
 			ddl += colStr + ";"
 			ddls = append(ddls, ddl)
 			if item.After.Default != nil {
-				ddls = append(
-					ddls,
-					fmt.Sprintf("ALTER TABLE `%s` ALTER COLUMN `%s` SET DEFAULT %s;", tableFullName, item.After.Name, getDefaultString(item.After.Default)),
-					fmt.Sprintf("UPDATE `%s` SET `%s` = %s WHERE TRUE;", tableFullName, item.After.Name, getDefaultString(item.After.Default)),
-				)
-
+				return nil, errors.New("BigQuery currently does not support add column with default value")
 			} else if item.After.Nullable == "true" {
 				ddls = append(ddls, fmt.Sprintf("ALTER TABLE `%s` ALTER COLUMN `%s` SET DEFAULT NULL;", tableFullName, item.After.Name))
 			}
@@ -110,14 +97,6 @@ func GenDDLViaColumnsDiff(datasetID, tableID string, prevColumns []cloudstorage.
 	return ddls, nil
 }
 
-func getDefaultString(val interface{}) string {
-	_, err := strconv.ParseFloat(fmt.Sprintf("%v", val), 64)
-	if err != nil {
-		return fmt.Sprintf("'%v'", val) // FIXME: escape
-	}
-	return fmt.Sprintf("%v", val)
-}
-
 // GetBigQueryColumnString returns a string describing the column in BigQuery, e.g.
 // "id INT NOT NULL DEFAULT '0'"
 // Refer to:
@@ -131,9 +110,7 @@ func GetBigQueryColumnString(column cloudstorage.TableCol, createTable bool) (st
 	}
 	sb.WriteString(fmt.Sprintf("`%s` %s", column.Name, colType))
 	if createTable {
-		if column.Default != nil {
-			sb.WriteString(fmt.Sprintf(` DEFAULT %s`, getDefaultString(column.Default)))
-		} else if column.Nullable == "true" {
+		if column.Nullable == "true" {
 			sb.WriteString(" DEFAULT NULL")
 		}
 	}