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 100

2、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 100

3、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 100

3、postgresql中函数调用

select 'sys_dept' AS table,showcreatetable('public','sys_dept') AS create_table

4、实现效果