PostgreSQL教程--实现类似于MySQL的show create table功能
背景
在MySQL数据库中，可以通过show create table查询表的create sql 语句，
但在PostgreSQL数据库中，没有类似的命令，但可以通过function 来实现
1、show create table函数
CREATE OR REPLACE FUNCTION "public"."showcreatetable"("namespace" varchar, "tablename" varchar)
RETURNS "pg_catalog"."varchar" AS $BODY$
declare
tableScript character varying default '';
begin
-- columns
tableScript:=tableScript || ' CREATE TABLE '|| tablename|| ' ( '|| chr(13)||chr(10) || array_to_string(
array(
select ' ' || concat_ws(' ',fieldName, fieldType, fieldLen, indexType, isNullStr, fieldComment ) as column_line
from (
select a.attname as fieldName,format_type(a.atttypid,a.atttypmod) as fieldType,' ' as fieldLen,
'' as indexType,
(case when a.attnotnull=true then 'not null' else 'null' end) as isNullStr,
' 'as fieldComment
from pg_attribute a where attstattarget=-1 and attrelid = (select c.oid from pg_class c,pg_namespace n where c.relnamespace=n.oid and n.nspname =namespace and relname =tablename)
) as string_columns
),','||chr(13)||chr(10)) || ',';
-- 约束
tableScript:= tableScript || chr(13)||chr(10) || array_to_string(
array(
select concat(' CONSTRAINT ',conname ,c ,u,p,f) from (
select conname,
case when contype='c' then ' CHECK('|| ( select findattname(namespace,tablename,'c') ) ||')' end as c ,
case when contype='u' then ' UNIQUE('|| ( select findattname(namespace,tablename,'u') ) ||')' end as u ,
case when contype='p' then ' PRIMARY KEY ('|| ( select findattname(namespace,tablename,'p') ) ||')' end as p ,
case when contype='f' then ' FOREIGN KEY('|| ( select findattname(namespace,tablename,'u') ) ||') REFERENCES '||
(select p.relname from pg_class p where p.oid=c.confrelid ) || '('|| ( select findattname(namespace,tablename,'u') ) ||')' end as f
from pg_constraint c
where contype in('u','c','f','p') and conrelid=(
select oid from pg_class where relname=tablename and relnamespace =(
select oid from pg_namespace where nspname = namespace
)
)
) as t
) ,',' || chr(13)||chr(10) ) || chr(13)||chr(10) ||' ); ';
-- indexs
-- CREATE UNIQUE INDEX pg_language_oid_index ON pg_language USING btree (oid); -- table pg_language
--
/** **/
--- 获取非约束索引 column
-- CREATE UNIQUE INDEX pg_language_oid_index ON pg_language USING btree (oid); -- table pg_language
tableScript:= tableScript || chr(13)||chr(10) || chr(13)||chr(10) || array_to_string(
array(
select 'CREATE INDEX ' || indexrelname || ' ON ' || tablename || ' USING btree '|| '(' || attname || ');' from (
SELECT
i.relname AS indexrelname , x.indkey,
( select array_to_string (
array(
select a.attname from pg_attribute a where attrelid=c.oid and a.attnum in ( select unnest(x.indkey) )
)
,',' ) )as attname
FROM pg_class c
JOIN pg_index x ON c.oid = x.indrelid
JOIN pg_class i ON i.oid = x.indexrelid
LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE c.relname=tablename and i.relname not in
( select constraint_name from information_schema.key_column_usage where table_name=tablename )
)as t
) ,','|| chr(13)||chr(10));
-- COMMENT COMMENT ON COLUMN sys_activity.id IS '主键';
tableScript:= tableScript || chr(13)||chr(10) || chr(13)||chr(10) || array_to_string(
array(
SELECT 'COMMENT ON COLUMN ' || tablename || '.' || a.attname ||' IS '|| ''''|| d.description ||''''
FROM pg_class c
JOIN pg_description d ON c.oid=d.objoid
JOIN pg_attribute a ON c.oid = a.attrelid
WHERE c.relname=tablename
AND a.attnum = d.objsubid),';'|| chr(13)||chr(10)) ;
return tableScript;
end
$BODY$
LANGUAGE plpgsql VOLATILE
COST 1002、findattname函数
CREATE OR REPLACE FUNCTION "public"."findattname"("namespace" varchar, "tablename" varchar, "ctype" varchar)
RETURNS "pg_catalog"."varchar" AS $BODY$
declare
tt oid ;
aname character varying default '';
begin
tt := oid from pg_class where relname= tablename and relnamespace =(select oid from pg_namespace where nspname=namespace) ;
aname:= array_to_string(
array(
select a.attname from pg_attribute a
where a.attrelid=tt and a.attnum in (
select unnest(conkey) from pg_constraint c where contype=ctype
and conrelid=tt and array_to_string(conkey,',') is not null
)
),',');
return aname;
end
$BODY$
LANGUAGE plpgsql VOLATILE
COST 1003、generate_create_table_statement函数
CREATE OR REPLACE FUNCTION "public"."generate_create_table_statement"("p_table_name" varchar)
RETURNS "pg_catalog"."text" AS $BODY$
DECLARE
v_table_ddl text;
column_record record;
BEGIN
FOR column_record IN
SELECT
b.nspname as schema_name,
b.relname as table_name,
a.attname as column_name,
pg_catalog.format_type(a.atttypid, a.atttypmod) as column_type,
CASE WHEN
(SELECT substring(pg_catalog.pg_get_expr(d.adbin, d.adrelid) for 128)
FROM pg_catalog.pg_attrdef d
WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef) IS NOT NULL THEN
'DEFAULT '|| (SELECT substring(pg_catalog.pg_get_expr(d.adbin, d.adrelid) for 128)
FROM pg_catalog.pg_attrdef d
WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef)
ELSE
''
END as column_default_value,
CASE WHEN a.attnotnull = true THEN
'NOT NULL'
ELSE
'NULL'
END as column_not_null,
a.attnum as attnum,
e.max_attnum as max_attnum
FROM
pg_catalog.pg_attribute a
INNER JOIN
(SELECT c.oid,
n.nspname,
c.relname
FROM pg_catalog.pg_class c
LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
WHERE c.relname ~ ('^('||p_table_name||')$')
AND pg_catalog.pg_table_is_visible(c.oid)
ORDER BY 2, 3) b
ON a.attrelid = b.oid
INNER JOIN
(SELECT
a.attrelid,
max(a.attnum) as max_attnum
FROM pg_catalog.pg_attribute a
WHERE a.attnum > 0
AND NOT a.attisdropped
GROUP BY a.attrelid) e
ON a.attrelid=e.attrelid
WHERE a.attnum > 0
AND NOT a.attisdropped
ORDER BY a.attnum
LOOP
IF column_record.attnum = 1 THEN
v_table_ddl:='CREATE TABLE '||column_record.schema_name||'.'||column_record.table_name||' (';
ELSE
v_table_ddl:=v_table_ddl||',';
END IF;
IF column_record.attnum <= column_record.max_attnum THEN
v_table_ddl:=v_table_ddl||chr(10)||
' '||column_record.column_name||' '||column_record.column_type||' '||column_record.column_default_value||' '||column_record.column_not_null;
END IF;
END LOOP;
v_table_ddl:=v_table_ddl||');';
RETURN v_table_ddl;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 1003、postgresql中函数调用
select 'sys_dept' AS table,showcreatetable('public','sys_dept') AS create_table4、实现效果
