MySQL table 名称按依赖顺序排序

Question

我想获得 table 个按依赖顺序排序的名称。

例如：如果我有 table users、users_orders 和 orders 我想得到 table 这个顺序的名字：users（或orders无所谓），orders，users_orders。

如果有办法请帮忙

Answer 1

听起来您正在尝试转储具有外键定义的 tables，并且您想确保首先转储 "parent" tables，因此 "child" table 可以确保引用它们的外键定义有效。

一般不能这样做，因为循环依赖是可能的。

例如，如果您有 users 和 teams，其中每个用户都引用了他们所属的团队，但 teams 也引用了 captain对于作为队长的特定用户，您要先列出 users，还是先列出 teams？

另一种解决方案是以您想要的任何顺序输出所有 table，但没有外键定义。在列出所有 table 及其数据之后，然后使用 ALTER TABLE...ADD FOREIGN KEY 命令。

另一种替代解决方案（mysqldump 使用的解决方案）是在开头 SET FOREIGN_KEY_CHECKS=0。然后你可以定义外键约束而不用担心引用的 table 是否已经创建。 table 按字母顺序转储。

但更直接地回答您的问题：您可以使用 INFORMATION_SCHEMA 来发现存在哪些 table 依赖项。

SELECT table_schema, table_name, 
  GROUP_CONCAT(column_name ORDER BY ordinal_position) AS `columns`,
  MAX(referenced_table_schema) AS referenced_table_schema,
  MAX(referenced_table_name) AS referenced_table_name,
  GROUP_CONCAT(referenced_column_name ORDER BY ordinal_position) AS `ref_columns`
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE referenced_table_schema IS NOT NULL
GROUP BY table_schema, table_name;

MySQL 在 MySQL 8.0（仍在开发中）之前不支持递归查询。因此，您可能必须将依赖项数据提取到您的应用程序中，并确定要转储它们的顺序。

但是您仍然无法以这种方式处理循环。您必须使用我上面描述的替代方法之一。

Answer 2

你可以这样做。

获取所有 table 没有外键依赖项的列表。

SELECT TABLE_NAME
FROM information_schema.tables
WHERE table_schema='my_database'
  AND TABLE_NAME NOT IN (
  SELECT DISTINCT TABLE_NAME
  FROM information_schema.key_column_usage WHERE table_schema='my_database'
  AND referenced_table_name IS NOT NULL;

获取 table 的列表，这些 table 对另一个没有外键依赖的 table 具有外键依赖性。

SELECT DISTINCT TABLE_NAME
FROM information_schema.referential_constraints
WHERE CONSTRAINT_SCHEMA='my_database'
  AND referenced_table_name NOT IN
    (SELECT DISTINCT TABLE_NAME
     FROM information_schema.table_constraints
     WHERE constraint_type = 'FOREIGN KEY')
  AND TABLE_NAME NOT IN
    (SELECT DISTINCT TABLE_NAME
     FROM information_schema.referential_constraints
     WHERE referenced_table_name IN
         (SELECT DISTINCT TABLE_NAME
          FROM information_schema.table_constraints
          WHERE constraint_type = 'FOREIGN KEY'));

获取具有外键依赖性的 table 的列表，这些 table 本身具有外键依赖性。

SELECT DISTINCT TABLE_NAME
FROM information_schema.referential_constraints
WHERE CONSTRAINT_SCHEMA='my_database'
  AND referenced_table_name IN
    (SELECT DISTINCT TABLE_NAME
     FROM information_schema.table_constraints
     WHERE constraint_type = 'FOREIGN KEY');

然后您可以在如下脚本中使用它们。它不会解决上述循环依赖问题，但会创建一个 MySQL 转储文件，其中 table 按外键依赖排序。

#!/usr/bin/env bash
#
# staged-mysqldump.sh
#
# Runs mysqldump against a database and splits the output into
# three directories.
#
# <database_name>-STAGE-1 contains dumps of all of the tables
# that don't have any foreign key constraints.
# <database_name>-STAGE-2 contains dumps of all of the tables
# that have only have foreign key constraints with other tables
# that don't have foreign key constraints.
# <database_name>-STAGE-3 contains dumps of the rest of the tables.
#
#
DATABASE=""
DUMPDIR="/var/tmp"
MYSQL_CREDENTIALS="~/.my.cnf"
DUMPDATE="$(date +%Y%m%d)"
#
# Write a statement that drops the database if it exists and
# then write a create database statement to simulate a regular
# mysqldump.
#
echo "DROP DATABASE IF EXISTS $DATABASE;" >> $DUMPDIR/$DATABASE-$DUMPDATE-dump.sql
mysql --defaults-extra-file=$MYSQL_CREDENTIALS --skip-column-names --batch --execute "SHOW CREATE DATABASE $DATABASE" | sed "s/^$DATABASE\s\+//;s/$/;/" >> $DUMPDIR/$DATABASE-$DUMPDATE-dump.sql
#
# Dump the stage 1 tables.
#
printf "Dumping tables for %s - Stage 1\n" "$DATABASE"
STAGE_1_TABLES=$(mysql --defaults-extra-file=$MYSQL_CREDENTIALS --skip-column-names --batch --execute "SELECT table_name FROM information_schema.tables WHERE table_schema='$DATABASE' AND table_name NOT IN (SELECT distinct table_name FROM information_schema.key_column_usage WHERE table_schema='$DATABASE' AND referenced_table_name IS NOT NULL)")
printf "Stage 1 Start Time: %(%Y-%m-%d - %H:%M:%S)T\n"
mysqldump --defaults-extra-file=$MYSQL_CREDENTIALS --databases $DATABASE --tables $STAGE_1_TABLES >> $DUMPDIR/$DATABASE-$DUMPDATE-dump.sql
printf "Finished dumping tables for %s - Stage 1\n" "$DATABASE"
printf "Stage 1 End Time: %(%Y-%m-%d - %H:%M:%S)T\n"
#
# Dump the stage 2 tables.
#
printf "Dumping tables for %s - Stage 2\n" "$DATABASE"
STAGE_2_TABLES=$(mysql --defaults-extra-file=$MYSQL_CREDENTIALS --skip-column-names --batch --execute "SELECT DISTINCT table_name FROM information_schema.referential_constraints WHERE constraint_schema='$DATABASE' AND referenced_table_name NOT IN (SELECT DISTINCT table_name FROM information_schema.table_constraints WHERE constraint_type = 'FOREIGN KEY') AND table_name NOT IN (SELECT DISTINCT table_name FROM information_schema.referential_constraints WHERE referenced_table_name IN (SELECT DISTINCT table_name FROM information_schema.table_constraints WHERE constraint_type = 'FOREIGN KEY'))")
printf "Stage 2 Start Time: %(%Y-%m-%d - %H:%M:%S)T\n"
mysqldump --defaults-extra-file=$MYSQL_CREDENTIALS --databases $DATABASE --tables $STAGE_2_TABLES >> $DUMPDIR/$DATABASE-$DUMPDATE-dump.sql
printf "Finished dumping tables for %s - Stage 2\n" "$DATABASE"
printf "Stage 2 End Time: %(%Y-%m-%d - %H:%M:%S)T\n"
#
# Dump the stage 3 tables.
#
printf "Dumping tables for %s - Stage 3\n" "$DATABASE"
STAGE_3_TABLES=$(mysql --defaults-extra-file=$MYSQL_CREDENTIALS --skip-column-names --batch --execute "SELECT DISTINCT table_name FROM information_schema.referential_constraints WHERE constraint_schema='$DATABASE' AND referenced_table_name IN (SELECT DISTINCT table_name FROM information_schema.table_constraints WHERE constraint_type = 'FOREIGN KEY')")
printf "Stage 3 Start Time: %(%Y-%m-%d - %H:%M:%S)T\n"
mysqldump --defaults-extra-file=$MYSQL_CREDENTIALS --databases $DATABASE --tables $STAGE_2_TABLES >> $DUMPDIR/$DATABASE-$DUMPDATE-dump.sql
printf "Finished dumping tables for %s - Stage 3\n" "$DATABASE"
printf "Stage 3 End Time: %(%Y-%m-%d - %H:%M:%S)T\n"

如果您使用它，您可能需要调整传递给 MySQL 的选项。

MySQL table 名称按依赖顺序排序

MySQL table names ordered by dependency order

mysql

foreign-keys

database-schema