sqlite

Database; use; embedded relational database

explain

英[ɪkˈspleɪn] 美[ɪkˈsplen ]

vt.& vi. explain, explain

vt.explain the reasons for, defend

vi.explain, explain, defend

SQLite Explain function syntax

Function:Before the SQLite statement, you can use the "EXPLAIN" keyword or the "EXPLAIN QUERY PLAN" phrase to describe the details of the table. If the EXPLAIN keyword or phrase is omitted, any modification will cause the query behavior of the SQLite statement to return information about how the SQLite statement operates. Output from EXPLAIN and EXPLAIN QUERY PLAN is used only for interactive analysis and troubleshooting. The details of the output format may vary between SQLite versions. Applications should not use EXPLAIN or EXPLAIN QUERY PLAN because their exact behavior is variable and only partially logged.

Grammar: The syntax of EXPLAIN is as follows:

EXPLAIN [SQLite Query]

The syntax of EXPLAIN QUERY PLAN is as follows:

EXPLAIN QUERY PLAN [SQLite Query]

SQLite Explain function example

假设 COMPANY 表有以下记录：

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           James       24          Houston     10000.0
现在，让我们检查 SELECT 语句中的 Explain 使用：

sqlite> EXPLAIN SELECT *  FROM COMPANY  WHERE Salary >= 20000;
这将产生以下结果：

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，让我们检查 SELECT 语句中的 Explain Query Plan 使用：

SQLite> EXPLAIN QUERY PLAN SELECT * FROM COMPANY WHERE Salary >= 20000;
order       from        detail
----------  ----------  -------------
0           0           TABLE COMPANY