DESCRIBE

功能描述

DESCRIBE 和 EXPLAIN 互为同义词，可以用于查看指定表结构，或查看指定 SQL 的执行计划。

查看执行计划部分内容详见 EXPLAIN。

注意事项

  • 临时表需要指定临时表对应的schema查询。
  • 复合主键索引所有参与列都会在Key字段中显示为PRI。
  • 复合唯一索引所有参与列都会在Key字段中显示为UNI。
  • 如果一个列参与了多个索引的创建，将按 PRI、UNI、MUL 的优先级顺序显示。
  • 生成列会在Default中显示生成式。
  • 不支持表同义词。

语法格式

  1. {DESCRIBE | DESC | EXPLAIN} tbl_name

参数说明

  • {DESCRIBE | DESC | EXPLAIN}

    1.  使用 DESCRIBE、DESC 和 EXPLAIN 效果是等价的。

  • tbl_name

    1.  表名，可指定表名。也可以指定schema_name.table_name。

示例

  1. --创建test表
  2. openGauss=# CREATE TABLE test2
  3. openGauss-# (
  4. openGauss(# id int PRIMARY KEY
  5. openGauss(# );
  6. NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test2_pkey" for table "test2"
  7. CREATE TABLE
  8. openGauss=# create table test
  9. openGauss-# (
  10. openGauss(# a SERIAL,
  11. openGauss(# b varchar(10),
  12. openGauss(# c varchar(10),
  13. openGauss(# d varchar(10),
  14. openGauss(# e varchar(10),
  15. openGauss(# f varchar(10),
  16. openGauss(# g varchar(10) DEFAULT 'g',
  17. openGauss(# h varchar(10) NOT NULL,
  18. openGauss(# i int DEFAULT 0,
  19. openGauss(# j int DEFAULT 0,
  20. openGauss(# k int GENERATED ALWAYS AS (i + j) STORED,
  21. openGauss(# l int DEFAULT 0,
  22. openGauss(# m int CHECK (m < 50),
  23. openGauss(# PRIMARY KEY (a, b),
  24. openGauss(# FOREIGN KEY(l) REFERENCES test2(id)
  25. openGauss(# );
  26. NOTICE:  CREATE TABLE will create implicit sequence "test_a_seq" for serial column "test.a"
  27. NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
  28. CREATE TABLE
  29. openGauss=# CREATE UNIQUE INDEX idx_c on test (c);
  30. CREATE INDEX
  31. openGauss=# CREATE UNIQUE INDEX idx_d_e on test (d, e);
  32. CREATE INDEX
  33. openGauss=# CREATE INDEX idx_f on test (f);
  34. CREATE INDEX
  36. --查看test表结构
  37. openGauss=# desc test;
  38.  Field |         Type          | Null | Key |             Default             | Extra
  39. -------+-----------------------+------+-----+---------------------------------+-------
  40.  a     | integer               | NO   | PRI | nextval('test_a_seq'::regclass) |
  41.  b     | character varying(10) | NO   | PRI | NULL                            |
  42.  c     | character varying(10) | YES  | UNI | NULL                            |
  43.  d     | character varying(10) | YES  | UNI | NULL                            |
  44.  e     | character varying(10) | YES  | UNI | NULL                            |
  45.  f     | character varying(10) | YES  | MUL | NULL                            |
  46.  g     | character varying(10) | YES  |     | 'g'::character varying          |
  47.  h     | character varying(10) | NO   |     | NULL                            |
  48.  i     | integer               | YES  |     | 0                               |
  49.  j     | integer               | YES  |     | 0                               |
  50.  k     | integer               | YES  |     | (i + j)                         |
  51.  l     | integer               | YES  | MUL | 0                               |
  52.  m     | integer               | YES  |     | NULL                            |
  53. (13 rows)
  55. openGauss=# desc public.test;
  56.  Field |         Type          | Null | Key |             Default             | Extra
  57. -------+-----------------------+------+-----+---------------------------------+-------
  58.  a     | integer               | NO   | PRI | nextval('test_a_seq'::regclass) |
  59.  b     | character varying(10) | NO   | PRI | NULL                            |
  60.  c     | character varying(10) | YES  | UNI | NULL                            |
  61.  d     | character varying(10) | YES  | UNI | NULL                            |
  62.  e     | character varying(10) | YES  | UNI | NULL                            |
  63.  f     | character varying(10) | YES  | MUL | NULL                            |
  64.  g     | character varying(10) | YES  |     | 'g'::character varying          |
  65.  h     | character varying(10) | NO   |     | NULL                            |
  66.  i     | integer               | YES  |     | 0                               |
  67.  j     | integer               | YES  |     | 0                               |
  68.  k     | integer               | YES  |     | (i + j)                         |
  69.  l     | integer               | YES  | MUL | 0                               |
  70.  m     | integer               | YES  |     | NULL                            |
  71. (13 rows)
  73. openGauss=# describe public.test;
  74.  Field |         Type          | Null | Key |             Default             | Extra
  75. -------+-----------------------+------+-----+---------------------------------+-------
  76.  a     | integer               | NO   | PRI | nextval('test_a_seq'::regclass) |
  77.  b     | character varying(10) | NO   | PRI | NULL                            |
  78.  c     | character varying(10) | YES  | UNI | NULL                            |
  79.  d     | character varying(10) | YES  | UNI | NULL                            |
  80.  e     | character varying(10) | YES  | UNI | NULL                            |
  81.  f     | character varying(10) | YES  | MUL | NULL                            |
  82.  g     | character varying(10) | YES  |     | 'g'::character varying          |
  83.  h     | character varying(10) | NO   |     | NULL                            |
  84.  i     | integer               | YES  |     | 0                               |
  85.  j     | integer               | YES  |     | 0                               |
  86.  k     | integer               | YES  |     | (i + j)                         |
  87.  l     | integer               | YES  | MUL | 0                               |
  88.  m     | integer               | YES  |     | NULL                            |
  89. (13 rows)

相关链接

EXPLAIN