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
{DESCRIBE | DESC | EXPLAIN} tbl_name
参数说明
{DESCRIBE | DESC | EXPLAIN}
使用 DESCRIBE、DESC 和 EXPLAIN 效果是等价的。
tbl_name
表名,可指定表名。也可以指定schema_name.table_name。
示例
--创建test表
openGauss=# CREATE TABLE test2
openGauss-# (
openGauss(# id int PRIMARY KEY
openGauss(# );
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "test2_pkey" for table "test2"
CREATE TABLE
openGauss=# create table test
openGauss-# (
openGauss(# a SERIAL,
openGauss(# b varchar(10),
openGauss(# c varchar(10),
openGauss(# d varchar(10),
openGauss(# e varchar(10),
openGauss(# f varchar(10),
openGauss(# g varchar(10) DEFAULT 'g',
openGauss(# h varchar(10) NOT NULL,
openGauss(# i int DEFAULT 0,
openGauss(# j int DEFAULT 0,
openGauss(# k int GENERATED ALWAYS AS (i + j) STORED,
openGauss(# l int DEFAULT 0,
openGauss(# m int CHECK (m < 50),
openGauss(# PRIMARY KEY (a, b),
openGauss(# FOREIGN KEY(l) REFERENCES test2(id)
openGauss(# );
NOTICE: CREATE TABLE will create implicit sequence "test_a_seq" for serial column "test.a"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
openGauss=# CREATE UNIQUE INDEX idx_c on test (c);
CREATE INDEX
openGauss=# CREATE UNIQUE INDEX idx_d_e on test (d, e);
CREATE INDEX
openGauss=# CREATE INDEX idx_f on test (f);
CREATE INDEX
--查看test表结构
openGauss=# desc test;
Field | Type | Null | Key | Default | Extra
-------+-----------------------+------+-----+---------------------------------+-------
a | integer | NO | PRI | nextval('test_a_seq'::regclass) |
b | character varying(10) | NO | PRI | NULL |
c | character varying(10) | YES | UNI | NULL |
d | character varying(10) | YES | UNI | NULL |
e | character varying(10) | YES | UNI | NULL |
f | character varying(10) | YES | MUL | NULL |
g | character varying(10) | YES | | 'g'::character varying |
h | character varying(10) | NO | | NULL |
i | integer | YES | | 0 |
j | integer | YES | | 0 |
k | integer | YES | | (i + j) |
l | integer | YES | MUL | 0 |
m | integer | YES | | NULL |
(13 rows)
openGauss=# desc public.test;
Field | Type | Null | Key | Default | Extra
-------+-----------------------+------+-----+---------------------------------+-------
a | integer | NO | PRI | nextval('test_a_seq'::regclass) |
b | character varying(10) | NO | PRI | NULL |
c | character varying(10) | YES | UNI | NULL |
d | character varying(10) | YES | UNI | NULL |
e | character varying(10) | YES | UNI | NULL |
f | character varying(10) | YES | MUL | NULL |
g | character varying(10) | YES | | 'g'::character varying |
h | character varying(10) | NO | | NULL |
i | integer | YES | | 0 |
j | integer | YES | | 0 |
k | integer | YES | | (i + j) |
l | integer | YES | MUL | 0 |
m | integer | YES | | NULL |
(13 rows)
openGauss=# describe public.test;
Field | Type | Null | Key | Default | Extra
-------+-----------------------+------+-----+---------------------------------+-------
a | integer | NO | PRI | nextval('test_a_seq'::regclass) |
b | character varying(10) | NO | PRI | NULL |
c | character varying(10) | YES | UNI | NULL |
d | character varying(10) | YES | UNI | NULL |
e | character varying(10) | YES | UNI | NULL |
f | character varying(10) | YES | MUL | NULL |
g | character varying(10) | YES | | 'g'::character varying |
h | character varying(10) | NO | | NULL |
i | integer | YES | | 0 |
j | integer | YES | | 0 |
k | integer | YES | | (i + j) |
l | integer | YES | MUL | 0 |
m | integer | YES | | NULL |
(13 rows)
相关链接
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