MySQL， SQLite 和 PostgreSQL 关于information_schema 的一些查询（表结构，表信息，库信息....）

显示（查询）所有的数据库

MySQL查询：

show databases

PostgreSQL查询：

select * from pg_database

查询当前数据库中所有的表信息

like后可写入模糊匹配的表名称

MySQL查询：

SELECT
	table_name tableName,
	ENGINE,
	table_comment tableComment,
	create_time createTime 
FROM
	information_schema.TABLES 
WHERE
	table_schema = ( SELECT DATABASE ( ) ) 
	AND table_name LIKE '%%' 
ORDER BY
	create_time DESC

show tables

PostgreSQL查询：

SELECT
	* 
FROM
	information_schema.TABLES 
WHERE
	table_schema = 'public' 
	AND table_name LIKE '%%'

SELECT
	n.nspname,
	relname 
FROM
	pg_class c,
	pg_namespace n 
WHERE
	c.relnamespace = n.oid 
	AND nspname = 'public' 
	AND relkind = 'r' 
ORDER BY
	relname;

SQLite 查询：

select * from sqlite_master where type = "table";

select * from sqlite_master where name = "表名称"

查询某一张表中的字段信息

MySQL查询：

SELECT
	column_name columnName,
	data_type dataType,
	column_comment columnComment,
	column_key columnKey,
	extra 
FROM
	information_schema.COLUMNS 
WHERE
	table_name = '表名称' 
	AND table_schema = ( SELECT DATABASE ( ) ) 
ORDER BY
	ordinal_position

desc 表名称

PostgreSQL查询：

SELECT
	* 
FROM
	information_schema.COLUMNS 
WHERE
	table_schema = 'public' 
	AND table_name = 表名称;

复杂一点的

SELECT
	col.table_schema,
	col.table_name,
	col.ordinal_position,
	col.column_name,
	col.data_type,
	col.character_maximum_length,
	col.numeric_precision,
	col.numeric_scale,
	col.is_nullable,
	col.column_default,
	des.description 
FROM
	information_schema.COLUMNS col
	LEFT JOIN pg_description des ON col.table_name :: regclass = des.objoid 
	AND col.ordinal_position = des.objsubid 
WHERE
	table_schema = 'public' 
	AND table_name = 表名称 
ORDER BY
	ordinal_position;

SQLite 查询：

PRAGMA table_info(表名称)