SQL*PLUS
在SQL*PLUS执行,会在执行后显示查询的执行计划和统计信息
sql
SET AUTOTRACE ON;
SELECT * FROM your_table WHERE column_name = 'value';
SET AUTOTRACE OFF;
PLSQL
PLSQL查询sql界面,鼠标右键,点击执行计划,会出现sql的执行计划结果
sql
SELECT * FROM your_table WHERE column_name = 'value';
oracle SQL查询表索引信息
sql
SELECT c.INDEX_NAME,
CASE UNIQUENESS
WHEN 'UNIQUE' THEN 'Unique Index'
WHEN 'NONUNIQUE' THEN 'Non-Unique Index'
ELSE 'Unknown'
END AS INDEX_TYPE,
LISTAGG(COLUMN_NAME, ', ') WITHIN GROUP (ORDER BY COLUMN_POSITION) AS INDEX_COLUMNS
FROM USER_IND_COLUMNS C
JOIN USER_INDEXES I ON C.TABLE_NAME = I.TABLE_NAME AND C.INDEX_NAME = I.INDEX_NAME
WHERE c.TABLE_NAME = '<table_name>'
GROUP BY c.INDEX_NAME, UNIQUENESS;
instr函数
instr(config_desc, ',')=0
其中如果config_desc为null,表达式的值为null,字符串未找到为0
sql
select instr(null,',');-- null
select instr('null',','); -- 0
select instr('null,null,',','); -- 0
unistr函数
Unicode转字符串
SELECT UNISTR('\00a0') from dual;
子查询
标量子查询
子查询的结果有且仅有一条
SELECT column1, (SELECT MAX(column2) FROM table2) AS max_value
FROM table1;
sql
--子查询结果不为1条
-- 列中子查询
select id,
(select password from users)
from users group by id;
-- where条件子查询
select id
from users where id > (select id from users)
表子查询
执行顺序优于主查询
SELECT column1
FROM (SELECT column2 FROM table2 WHERE condition) AS subquery;