sintaxis - ¿Cómo se usa la cláusula "CON" en MySQL?

having en mysql

Question

Estoy convirtiendo todas mis consultas de SQL Server a MySQL y mis consultas que tienen WITH en todos fallan. Aquí hay un ejemplo:

WITH t1 AS
(
SELECT article.*, userinfo.*, category.*
FROM question
INNER JOIN userinfo ON userinfo.user_userid = article.article_ownerid
INNER JOIN category ON article.article_categoryid = category.catid
WHERE article.article_isdeleted = 0
)
SELECT t1.*
FROM t1
ORDER BY t1.article_date DESC
LIMIT 1, 3

Answer 1

El equipo de desarrolladores de Mysql anunció que la versión 8.0 tendrá Expresiones de tabla comunes en MySQL (CTE) . Por lo tanto, será posible escribir consultas como esta:

WITH RECURSIVE my_cte AS
(
SELECT 1 AS n
UNION ALL
SELECT 1+n FROM my_cte WHERE n<10
)
SELECT * FROM my_cte;
+------+
| n |
+------+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
| 10 |
+------+
10 rows in set (0,00 sec)

Answer 2

En Sql, la sentencia with especifica un conjunto de resultados con nombre temporal, conocido como expresión de tabla común (CTE). Se puede usar para consultas recursivas, pero en este caso, se especifica como subconjunto. Si mysql permite subselectes lo intentaría

select t1.*
from (
SELECT article.*,
userinfo.*,
category.*
FROM question INNER JOIN
userinfo ON userinfo.user_userid=article.article_ownerid INNER JOIN category ON article.article_categoryid=category.catid
WHERE article.article_isdeleted = 0
) t1
ORDER BY t1.article_date DESC Limit 1, 3

Answer 3

Esa característica se denomina expresión de tabla común http://msdn.microsoft.com/en-us/library/ms190766.aspx

No podrá hacer exactamente lo mismo en mySQL, lo más fácil sería probablemente hacer una vista que refleje ese CTE y simplemente seleccionar desde la vista. Puedes hacerlo con subconsultas, pero funcionará muy mal. Si se encuentra con CTE que hacen recursividad, no sé cómo podría recrear eso sin utilizar procedimientos almacenados.

EDITAR: Como dije en mi comentario, ese ejemplo que publicó no tiene necesidad de un CTE, por lo que debe haberlo simplificado para la pregunta, ya que puede escribirse como

SELECT article.*, userinfo.*, category.* FROM question
INNER JOIN userinfo ON userinfo.user_userid=article.article_ownerid
INNER JOIN category ON article.article_categoryid=category.catid
WHERE article.article_isdeleted = 0
ORDER BY article_date DESC Limit 1, 3

Answer 4

La característica ''Common Table Expression'' no está disponible en MySQL, por lo que tiene que ir a hacer una vista o tabla temporal para resolver, aquí he usado una tabla temporal.

El procedimiento almacenado mencionado aquí resolverá su necesidad. Si quiero obtener todos los miembros de mi equipo y sus miembros asociados, este procedimiento almacenado ayudará:

----------------------------------
user_id | team_id
----------------------------------
admin | NULL
ramu | admin
suresh | admin
kumar | ramu
mahesh | ramu
randiv | suresh
-----------------------------------

Código:

DROP PROCEDURE `user_hier`//
CREATE DEFINER=`root`@`localhost` PROCEDURE `user_hier`(in team_id varchar(50))
BEGIN
declare count int;
declare tmp_team_id varchar(50);
CREATE TEMPORARY TABLE res_hier(user_id varchar(50),team_id varchar(50))engine=memory;
CREATE TEMPORARY TABLE tmp_hier(user_id varchar(50),team_id varchar(50))engine=memory;
set tmp_team_id = team_id;
SELECT COUNT(*) INTO count FROM user_table WHERE user_table.team_id=tmp_team_id;
WHILE count>0 DO
insert into res_hier select user_table.user_id,user_table.team_id from user_table where user_table.team_id=tmp_team_id;
insert into tmp_hier select user_table.user_id,user_table.team_id from user_table where user_table.team_id=tmp_team_id;
select user_id into tmp_team_id from tmp_hier limit 0,1;
select count(*) into count from tmp_hier;
delete from tmp_hier where user_id=tmp_team_id;
end while;
select * from res_hier;
drop temporary table if exists res_hier;
drop temporary table if exists tmp_hier;
end

Esto se puede llamar usando:

mysql>call user_hier (''admin'')//

Answer 5

Seguí el enlace compartido por lisachenko y encontré otro enlace a este blog: http://guilhembichot.blogspot.co.uk/2013/11/with-recursive-and-mysql.html

La publicación establece formas de emular los 2 usos de SQL WITH. Explicación muy buena sobre cómo funcionan para hacer una consulta similar a SQL WITH.

1) Use WITH para que no tenga que realizar la misma sub consulta varias veces

CREATE VIEW D AS (SELECT YEAR, SUM(SALES) AS S FROM T1 GROUP BY YEAR);
SELECT D1.YEAR, (CASE WHEN D1.S>D2.S THEN ''INCREASE'' ELSE ''DECREASE'' END) AS TREND
FROM
D AS D1,
D AS D2
WHERE D1.YEAR = D2.YEAR-1;
DROP VIEW D;

2) Las consultas recursivas se pueden realizar con un procedimiento almacenado que hace que la llamada sea similar a un recursivo con consulta.

CALL WITH_EMULATOR(
"EMPLOYEES_EXTENDED",
"
SELECT ID, NAME, MANAGER_ID, 0 AS REPORTS
FROM EMPLOYEES
WHERE ID NOT IN (SELECT MANAGER_ID FROM EMPLOYEES WHERE MANAGER_ID IS NOT NULL)
",
"
SELECT M.ID, M.NAME, M.MANAGER_ID, SUM(1+E.REPORTS) AS REPORTS
FROM EMPLOYEES M JOIN EMPLOYEES_EXTENDED E ON M.ID=E.MANAGER_ID
GROUP BY M.ID, M.NAME, M.MANAGER_ID
",
"SELECT * FROM EMPLOYEES_EXTENDED",
0,
""
);

Y este es el código o el procedimiento almacenado

# Usage: the standard syntax:
# WITH RECURSIVE recursive_table AS
# (initial_SELECT
# UNION ALL
# recursive_SELECT)
# final_SELECT;
# should be translated by you to
# CALL WITH_EMULATOR(recursive_table, initial_SELECT, recursive_SELECT,
# final_SELECT, 0, "").
# ALGORITHM:
# 1) we have an initial table T0 (actual name is an argument
# "recursive_table"), we fill it with result of initial_SELECT.
# 2) We have a union table U, initially empty.
# 3) Loop:
# add rows of T0 to U,
# run recursive_SELECT based on T0 and put result into table T1,
# if T1 is empty
# then leave loop,
# else swap T0 and T1 (renaming) and empty T1
# 4) Drop T0, T1
# 5) Rename U to T0
# 6) run final select, send relult to client
# This is for *one* recursive table.
# It would be possible to write a SP creating multiple recursive tables.
delimiter |
CREATE PROCEDURE WITH_EMULATOR(
recursive_table varchar(100), # name of recursive table
initial_SELECT varchar(65530), # seed a.k.a. anchor
recursive_SELECT varchar(65530), # recursive member
final_SELECT varchar(65530), # final SELECT on UNION result
max_recursion int unsigned, # safety against infinite loop, use 0 for default
create_table_options varchar(65530) # you can add CREATE-TABLE-time options
# to your recursive_table, to speed up initial/recursive/final SELECTs; example:
# "(KEY(some_column)) ENGINE=MEMORY"
)
BEGIN
declare new_rows int unsigned;
declare show_progress int default 0; # set to 1 to trace/debug execution
declare recursive_table_next varchar(120);
declare recursive_table_union varchar(120);
declare recursive_table_tmp varchar(120);
set recursive_table_next = concat(recursive_table, "_next");
set recursive_table_union = concat(recursive_table, "_union");
set recursive_table_tmp = concat(recursive_table, "_tmp");
# Cleanup any previous failed runs
SET @str =
CONCAT("DROP TEMPORARY TABLE IF EXISTS ", recursive_table, ",",
recursive_table_next, ",", recursive_table_union,
",", recursive_table_tmp);
PREPARE stmt FROM @str;
EXECUTE stmt;
# If you need to reference recursive_table more than
# once in recursive_SELECT, remove the TEMPORARY word.
SET @str = # create and fill T0
CONCAT("CREATE TEMPORARY TABLE ", recursive_table, " ",
create_table_options, " AS ", initial_SELECT);
PREPARE stmt FROM @str;
EXECUTE stmt;
SET @str = # create U
CONCAT("CREATE TEMPORARY TABLE ", recursive_table_union, " LIKE ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
SET @str = # create T1
CONCAT("CREATE TEMPORARY TABLE ", recursive_table_next, " LIKE ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
if max_recursion = 0 then
set max_recursion = 100; # a default to protect the innocent
end if;
recursion: repeat
# add T0 to U (this is always UNION ALL)
SET @str =
CONCAT("INSERT INTO ", recursive_table_union, " SELECT * FROM ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# we are done if max depth reached
set max_recursion = max_recursion - 1;
if not max_recursion then
if show_progress then
select concat("max recursion exceeded");
end if;
leave recursion;
end if;
# fill T1 by applying the recursive SELECT on T0
SET @str =
CONCAT("INSERT INTO ", recursive_table_next, " ", recursive_SELECT);
PREPARE stmt FROM @str;
EXECUTE stmt;
# we are done if no rows in T1
select row_count() into new_rows;
if show_progress then
select concat(new_rows, " new rows found");
end if;
if not new_rows then
leave recursion;
end if;
# Prepare next iteration:
# T1 becomes T0, to be the source of next run of recursive_SELECT,
# T0 is recycled to be T1.
SET @str =
CONCAT("ALTER TABLE ", recursive_table, " RENAME ", recursive_table_tmp);
PREPARE stmt FROM @str;
EXECUTE stmt;
# we use ALTER TABLE RENAME because RENAME TABLE does not support temp tables
SET @str =
CONCAT("ALTER TABLE ", recursive_table_next, " RENAME ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
SET @str =
CONCAT("ALTER TABLE ", recursive_table_tmp, " RENAME ", recursive_table_next);
PREPARE stmt FROM @str;
EXECUTE stmt;
# empty T1
SET @str =
CONCAT("TRUNCATE TABLE ", recursive_table_next);
PREPARE stmt FROM @str;
EXECUTE stmt;
until 0 end repeat;
# eliminate T0 and T1
SET @str =
CONCAT("DROP TEMPORARY TABLE ", recursive_table_next, ", ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# Final (output) SELECT uses recursive_table name
SET @str =
CONCAT("ALTER TABLE ", recursive_table_union, " RENAME ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# Run final SELECT on UNION
SET @str = final_SELECT;
PREPARE stmt FROM @str;
EXECUTE stmt;
# No temporary tables may survive:
SET @str =
CONCAT("DROP TEMPORARY TABLE ", recursive_table);
PREPARE stmt FROM @str;
EXECUTE stmt;
# We are done :-)
END|
delimiter ;

Answer 6

MySQL no es compatible con la cláusula WITH (CTE en el lenguaje SQL Server, Subquery Factoring en Oracle), por lo que le queda el uso de:

• Tablas TEMPORALES
• Tablas DERIVADAS
• vistas en línea (efectivamente lo que representa la cláusula WITH - son intercambiables)

La solicitud de la función se remonta a 2006.

Como se mencionó, proporcionó un ejemplo pobre: ​​no es necesario realizar una subselección si no está alterando el resultado de las columnas de ninguna manera:

 SELECT *
FROM ARTICLE t
JOIN USERINFO ui ON ui.user_userid = t.article_ownerid
JOIN CATEGORY c ON c.catid = t.article_categoryid
WHERE t.published_ind = 0
ORDER BY t.article_date DESC
LIMIT 1, 3

Aquí hay un mejor ejemplo:

SELECT t.name,
t.num
FROM TABLE t
JOIN (SELECT c.id
COUNT(*) ''num''
FROM TABLE c
WHERE c.column = ''a''
GROUP BY c.id) ta ON ta.id = t.id