Overview
SQLite is an embedded relational DBMS, which is a library that runs in the same process as the application using it.
SQLite supports a text format of query plans in its shell.
Example
CREATE TABLE t0 (c0 INT);
CREATE TABLE t1 (c0 INT);
CREATE TABLE t2 (c0 INT PRIMARY KEY);
INSERT INTO t0 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
INSERT INTO t2 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
Table format of the query plan
EXPLAIN QUERY PLAN SELECT t1.c0 FROM t0 JOIN t1 ON t0.c0 = t1.c0
WHERE t0.c0 < 100 GROUP BY t1.c0
UNION SELECT c0 FROM t2 WHERE c0 < 10;
The first phrase followed by a -- is an operation, and others are properties.
QUERY PLAN
`--COMPOUND QUERY
|--LEFT-MOST SUBQUERY
| |--SCAN t0
| |--SEARCH t1 USING AUTOMATIC COVERING INDEX (c0=?)
| `--USE TEMP B-TREE FOR GROUP BY
`--UNION USING TEMP B-TREE
`--SEARCH t2 USING COVERING INDEX sqlite_autoindex_t2_1 (c0<?)