SQLite - Explain

SQLite的语句之前，可以由“EXPLAIN”的关键字或短语“EXPLAIN QUERY PLAN”，用于描述表的细节。

EXPLAIN - 语法

EXPLAIN 的语法如下-

EXPLAIN [SQLite Query]

EXPLAIN QUERY PLAN 的语法如下-

EXPLAIN  QUERY PLAN [SQLite Query]

EXPLAIN - 示例

考虑 COMPANY 表，其中包含以下记录-

ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0
6           Kim         22          South-Hall  45000.0
7           Learnfk       24          Houston     10000.0

现在，让无涯教程使用SELECT语句检查以下子查询-

sqlite> EXPLAIN SELECT * FROM COMPANY WHERE Salary &gt= 20000;

这将产生以下输出。

addr        opcode      p1          p2          p3
----------  ----------  ----------  ----------  ----------
0           Goto        0           19
1           Integer     0           0
2           OpenRead    0           8
3           SetNumColu  0           5
4           Rewind      0           17
5           Column      0           4
6           RealAffini  0           0
7           Integer     20000       0
8           Lt          357         16          collseq(BI
9           Rowid       0           0
10          Column      0           1
11          Column      0           2
12          Column      0           3
13          Column      0           4
14          RealAffini  0           0
15          Callback    5           0
16          Next        0           5
17          Close       0           0
18          Halt        0           0
19          Transactio  0           0
20          VerifyCook  0           38
21          Goto        0           1
22          Noop        0           0

现在，让无涯教程使用SELECT语句检查以下解释查询计划:

SQLite> EXPLAIN QUERY PLAN SELECT * FROM COMPANY WHERE Salary >= 20000;

order       from        detail
----------  ----------  -------------
0           0           TABLE COMPANY