示例

• 删除部分数据

  --建表。
  gaussdb=# CREATE TABLE test_t1(col1 INT,col2 INT);
  gaussdb=# INSERT INTO test_t1 VALUES (1, 1), (2, 2), (3, 3), (4, 4), (4, 6);
  
  --删除表中部分记录。
  gaussdb=# DELETE FROM test_t1 WHERE col1 = 4;
  
  --查询。
  gaussdb=# SELECT * FROM test_t1;
   col1 | col2 
  ------+------
      1 |    1
      2 |    2
      3 |    3
  (3 rows)

• 删除所有数据

  --删除所有的数据。
  gaussdb=# DELETE FROM test_t1;
  
  --查询。
  gaussdb=# SELECT * FROM test_t1;
   col1 | col2 
  ------+------
  (0 rows)
  
  --删除表。
  gaussdb=# DROP TABLE test_t1;

• WITH [ RECURSIVE ] with_query [, ...]

  --创建学生表。
  gaussdb=# CREATE TABLE student(id INT,name varchar(50));
  
  --创建成绩表。
  gaussdb=# CREATE TABLE grade(id INT,score CHAR);
  
  gaussdb=# INSERT INTO student VALUES (1, 'tom'), (2, 'jerry'), (3, 'david');
  gaussdb=# INSERT INTO grade VALUES (1, 'A'), (2, 'B'), (3, 'b');
  
  --在学生表中删除id=2的数据同时删除该学生在成绩表中的数据。
  gaussdb=# WITH del_stu AS(DELETE FROM student WHERE id = 2 RETURNING id)
      DELETE FROM grade WHERE id = (SELECT id FROM del_stu);
  
  --查询数据。
  gaussdb=# SELECT * FROM student;
   id | name  
  ----+-------
    1 | tom
    3 | david
  (2 rows)
  
  gaussdb=# SELECT * FROM grade;
   id | score 
  ----+-------
    1 | A
    3 | b
  (2 rows)
  
  --删除表。
  gaussdb=# DROP TABLE grade;
  gaussdb=# DROP TABLE student;

• 删除视图或子查询

  示例1：删除子查询

  --创建SCHEMA。
  gaussdb=# CREATE SCHEMA del_subqry;
  CREATE SCHEMA
  gaussdb=# SET CURRENT_SCHEMA = 'del_subqry';
  SET
  
  --创建表并插入数据。
  gaussdb=# CREATE TABLE t1 (x1 int, y1 int);
  NOTICE:  The 'DISTRIBUTE BY' clause is not specified. Using 'x1' as the distribution column by default.
  HINT:  Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
  CREATE TABLE
  gaussdb=# CREATE TABLE t2 (x2 int PRIMARY KEY, y2 int);
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t2_pkey" for table "t2"
  CREATE TABLE
  gaussdb=# CREATE TABLE tdata (x INT PRIMARY KEY, y INT);
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "tdata_pkey" for table "tdata"
  CREATE TABLE
  gaussdb=# CREATE TABLE tinfo (z INT PRIMARY KEY, comm VARCHAR2(20));
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "tinfo_pkey" for table "tinfo"
  CREATE TABLE
  gaussdb=# INSERT INTO t1 VALUES (1, 1), (2, 2), (3, 3), (5, 5);
  INSERT 0 4
  gaussdb=# INSERT INTO t2 VALUES (1, 1), (2, 2), (3, 3), (5, 5);
  INSERT 0 4
  gaussdb=# INSERT INTO tdata VALUES (1, 1), (2, 2), (3, 3);
  INSERT 0 3
  gaussdb=# INSERT INTO tinfo VALUES (1,'one'), (2, 'two'), (3, 'three'), (5, 'wrong three');
  INSERT 0 4
  
  --通过子查询删除t1中的数据。
  gaussdb=# DELETE FROM (SELECT * FROM t1) where y1 = 3;
  DELETE 1
  
  --子查询带READ ONLY，无法删除数据。
  gaussdb=# DELETE FROM (SELECT * FROM t1 WITH READ ONLY) WHERE y1 = 1;
  ERROR:  cannot perform a DML operation on a read-only subquery.
  
  --对多表连接的子查询删除。
  gaussdb=# SELECT * FROM t1, t2 WHERE x1 = x2;
   x1 | y1 | x2 | y2
  ----+----+----+----
    1 |  1 |  1 |  1
    2 |  2 |  2 |  2
    5 |  5 |  5 |  5
  (3 rows)
  
  gaussdb=# DELETE FROM (SELECT * FROM t1, t2 WHERE x1 = x2) WHERE y2 = 5;
  DELETE 1
  gaussdb=# SELECT * FROM t1, t2 WHERE x1 = x2;
   x1 | y1 | x2 | y2
  ----+----+----+----
    1 |  1 |  1 |  1
    2 |  2 |  2 |  2
  (2 rows)
  
  --子查询带CHECK OPTION，tdata表重复，其中 td1不是保留键表，td2是保留键表。
  gaussdb=# DELETE FROM (SELECT td1.x x1, td1.y y1, td2.x x2, td2.y y2 FROM tdata td1, tdata td2, tinfo WHERE td2.y=tinfo.z AND td1.x=td2.y WITH CHECK OPTION) WHERE y1 = 2;
  ERROR:  cannot delete from view without exactly one key-preserved table
  
  --不带CHECK OPTION，创建同样结构的子查询，删除成功。
  gaussdb=# DELETE FROM (SELECT td1.x x1, td1.y y1, td2.x x2, td2.y y2 FROM tdata td1, tdata td2, tinfo WHERE td2.y=tinfo.z AND td1.x=td2.y) WHERE y1 = 2;
  DELETE 1
  --删除SCHEMA。
  gaussdb=# RESET CURRENT_SCHEMA;
  RESET
  gaussdb=# DROP SCHEMA del_subqry CASCADE;
  NOTICE:  drop cascades to 5 other objects
  DETAIL:  drop cascades to table del_subqry.t1
  drop cascades to table del_subqry.t2
  drop cascades to table del_subqry.tdata
  drop cascades to table del_subqry.tinfo
  drop cascades to view del_subqry.vv_wco
  DROP SCHEMA

  示例2： 删除视图

  --创建SCHEMA。
  gaussdb=# CREATE SCHEMA del_view;
  CREATE SCHEMA。
  gaussdb=# SET CURRENT_SCHEMA = 'del_view';
  SET
  
  --创建表并插入数据。
  gaussdb=# CREATE TABLE t1 (x1 int, y1 int);
  NOTICE:  The 'DISTRIBUTE BY' clause is not specified. Using 'x1' as the distribution column by default.
  HINT:  Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
  CREATE TABLE
  gaussdb=# CREATE TABLE t2 (x2 int PRIMARY KEY, y2 int);
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t2_pkey" for table "t2"
  CREATE TABLE
  gaussdb=# CREATE TABLE tdata (x INT PRIMARY KEY, y INT);
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "tdata_pkey" for table "tdata"
  CREATE TABLE
  gaussdb=# CREATE TABLE tinfo (z INT PRIMARY KEY, comm VARCHAR2(20));
  NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "tinfo_pkey" for table "tinfo"
  CREATE TABLE
  gaussdb=# INSERT INTO t1 VALUES (1, 1), (2, 2), (3, 3), (5, 5);
  INSERT 0 4
  gaussdb=# INSERT INTO t2 VALUES (1, 1), (2, 2), (3, 3), (5, 5);
  INSERT 0 4
  gaussdb=# INSERT INTO tdata VALUES (1, 1), (2, 2), (3, 3);
  INSERT 0 3
  gaussdb=# INSERT INTO tinfo VALUES (1,'one'), (2, 'two'), (3, 'three'), (5, 'wrong three');
  INSERT 0 4
  
  --创建单表视图。
  gaussdb=# CREATE VIEW v_del1 AS SELECT * FROM t1;
  CREATE VIEW
  gaussdb=# CREATE VIEW v_del_read AS SELECT * FROM t1 WITH READ ONLY;
  CREATE VIEW
  
  --通过视图删除t1中的数据。
  gaussdb=# DELETE FROM v_del1 where y1 = 3;
  DELETE 1
  
  --视图带READ ONLY，无法删除数据。
  gaussdb=# DELETE FROM v_del_read WHERE y1 = 1;
  ERROR:  cannot perform a DML operation on a read-only subquery.
  
  --创建多表连接视图。
  gaussdb=# CREATE VIEW vvt1t2 AS SELECT * FROM t1, t2 WHERE x1 = x2;
  CREATE VIEW
  gaussdb=# CREATE VIEW vv_dup AS SELECT td1.x x1, td1.y y1, td2.x x2, td2.y y2 FROM tdata td1, tdata td2, tinfo WHERE td2.y=tinfo.z AND td1.x=td2.y;
  CREATE VIEW
  gaussdb=# CREATE VIEW vv_dup_wco AS SELECT td1.x x1, td1.y y1, td2.x x2, td2.y y2 FROM tdata td1, tdata td2, tinfo WHERE td2.y=tinfo.z AND td1.x=td2.y WITH CHECK OPTION;
  CREATE VIEW
  
  --对多表连接的视图做删除操作。
  gaussdb=# SELECT * FROM vvt1t2;
   x1 | y1 | x2 | y2
  ----+----+----+----
    1 |  1 |  1 |  1
    2 |  2 |  2 |  2
    5 |  5 |  5 |  5
  (3 rows)
  
  gaussdb=# DELETE FROM vvt1t2 WHERE y2 = 5;
  DELETE 1
  
  gaussdb=# SELECT * FROM vvt1t2;
   x1 | y1 | x2 | y2
  ----+----+----+----
    1 |  1 |  1 |  1
    2 |  2 |  2 |  2
  (2 rows)
  
  --视图带CHECK OPTION，tdata表重复，其中 td1不是保留键表，td2是保留键表。
  gaussdb=# DELETE FROM vv_dup_wco WHERE y1 = 2;
  ERROR:  cannot delete from view without exactly one key-preserved table
  
  --不带CHECK OPTION，创建同样结构的视图，删除成功。
  gaussdb=# DELETE FROM vv_dup WHERE y1 = 2;
  DELETE 1
  
  --删除SCHEMA。
  gaussdb=# RESET CURRENT_SCHEMA;
  RESET
  gaussdb=# DROP SCHEMA del_view CASCADE;
  NOTICE:  drop cascades to 9 other objects
  DETAIL:  drop cascades to table del_view.t1
  drop cascades to table del_view.t2
  drop cascades to table del_view.tdata
  drop cascades to table del_view.tinfo
  drop cascades to view del_view.v_del1
  drop cascades to view del_view.v_del_read
  drop cascades to view del_view.vvt1t2
  drop cascades to view del_view.vv_dup
  drop cascades to view del_view.vv_dup_wco
  DROP SCHEMA