SQLite - EXPLAIN


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SQLite statement can be preceded by the keyword "EXPLAIN" or by the phrase "EXPLAIN QUERY PLAN" used for describing the details of a table.

Either modification causes the SQLite statement to behave as a query and to return information about how the SQLite statement would have operated if the EXPLAIN keyword or phrase had been omitted.

  • The output from EXPLAIN and EXPLAIN QUERY PLAN is intended for interactive analysis and troubleshooting only.

  • The details of the output format are subject to change from one release of SQLite to the next.

  • Applications should not use EXPLAIN or EXPLAIN QUERY PLAN since their exact behavior is variable and only partially documented.

Syntax

syntax for EXPLAIN is as follows −

EXPLAIN [SQLite Query]

syntax for EXPLAIN QUERY PLAN is as follows −

EXPLAIN  QUERY PLAN [SQLite Query]

Example

Consider COMPANY table with the following records −

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

Now, let us check the following sub-query with SELECT statement −

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

This will produce the following result.

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

Now, let us check the following Explain Query Plan with SELECT statement −

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

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


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