This document discusses SQLite usage including its advantages of being file-based and suitable for development and small applications. It also notes SQLite limitations such as lack of access control lists and allowing only one write at a time. It provides code examples for creating a SQLite database and table, preparing SQL statements, binding parameters, executing queries, and handling errors. It also covers topics like using indexes, time zone handling, debugging SQL, and dealing with busy databases.

1. SQLite usage

2. SQLite
● Good
○ File based
○ Development
○ Small
● Bad
○ No ACL
○ Performance
○ Alow only one write at a time

3. SQLite Flow
● Create DB/table/index
● Prepare SQL
● SQL bind
● SQL Query

4. Create DB/table/index
#define CMD_CREATE_DP_TABLE "CREATE TABLE IF NOT EXISTS `data_planner` ("
"`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,"
"`tx_bytes` bigint(20) NOT NULL,"
"`rx_bytes` bigint(20) NOT NULL,"
"`timestamp` datetime);"
#define CMD_CREATE_DP_INDEX "CREATE INDEX IF NOT EXISTS `timestamp_idx` ON
`data_planner` (`timestamp` DESC);"

5. Create DB/table/index
sqlite3 *db = NULL;
char *err_msg = NULL;
int ret = -1;
if (sqlite3_open(DATA_PLANNER_DB_PATH, &db) != SQLITE_OK) {
syslog(LOG_ERR, "Open sqlite fail: %s", DATA_PLANNER_DB_PATH);
goto out;
}
if (sqlite3_exec(db, CMD_CREATE_DP_TABLE, NULL, NULL, &err_msg) != SQLITE_OK) {
syslog(LOG_ERR, "Create data_planner table fail: %s", err_msg);
goto out;
}
if (err_msg) sqlite3_free(err_msg);

6. Create DB/table/index
if (sqlite3_exec(db, CMD_CREATE_DP_INDEX, NULL, NULL, &err_msg) != SQLITE_OK) {
syslog(LOG_ERR, "Create data_planner index fail: %s", err_msg);
goto out;
}
ret = 0;
out:
if (err_msg) sqlite3_free(err_msg);
if (db) sqlite3_close(db);
return ret;

7. Create DB/table/index
● Check if using index
● “EXPLAIN <your query>”
○ ex: EXPLAIN SELECT * FROM a WERHE name =
“1”;
○ Will show IdxRowid/IdxGE if apply index

8. Create DB/table/index
sqlite> explain select * from users where name='foo';
0|Trace|0|0|0||00|
1|String8|0|1|0|foo|00|
2|Goto|0|18|0||00|
3|OpenRead|0|2|0|2|00|
4|OpenRead|1|3|0|keyinfo(1,BINARY)|00|
5|IsNull|1|15|0||00|
6|Affinity|1|1|0|bb|00|
7|SeekGe|1|15|1|1|00|
8|IdxGE|1|15|1|1|01|
9|IdxRowid|1|2|0||00|
...blahblah
21|Goto|0|3|0||00|

9. Create DB/table/index
● When to create?
○ System startup
○ Program startup
○ In every query

10. Prepare SQL
sqlite3 *db = NULL;
sqlite3_stmt *stmt = NULL;
int ret = DP_ERROR;
if (sqlite3_open(DATA_PLANNER_DB_PATH, &db) != SQLITE_OK) {
syslog(LOG_ERR, "Open sqlite fail: %s", DATA_PLANNER_DB_PATH);
goto out;
}
char *sql = "SELECT sum(tx_bytes) as total_tx_bytes,sum(rx_bytes) as total_rx_bytes
FROM data_planner WHERE datetime(timestamp, 'localtime') >= ? AND datetime(timestamp, 'localtime') < ?;";
if (sqlite3_prepare_v2(db, sql, strlen(sql), &stmt, NULL) != SQLITE_OK) {
syslog(LOG_ERR, "SQL prepare fail: %s", sql);
goto out;
}

11. SQL Bind
sqlite3_bind_text(stmt, 1, begin_date, -1, NULL);
sqlite3_bind_text(stmt, 2, end_date, -1, NULL);
// Also, there is no uint64, only int64

12. SQL Query
if (sqlite3_step(stmt) == SQLITE_ROW) {
*total_tx_bytes = sqlite3_column_int64(stmt, 0);
*total_rx_bytes = sqlite3_column_int64(stmt, 1);
} else {
syslog(LOG_ERR, "SQL fail: Error when get previous total data: %s", sqlite3_errmsg(db));
goto out;
}
ret = 0;
out:
if (stmt) sqlite3_finalize(stmt);
if (db) sqlite3_close(db);
return ret;

13. SQL Query
● sqlite3_exec
○ sqlite3_prepare_v2 + sqlite3_step + sqlite3_finalize
○ Good for insertion/create table/transaction
○ Bad for query

14. SQL Query
sqlite3_exec(
sqlite3*,
const char *sql,
int (*callback)(void*, int column_num, char**, char**),
void *,
char **errmsg
}
// void * is for user data

15. Timezone issue
● Use UTC
● In C
○ Use gmtime_r instead of localtime_r
● In SQLite3
○ Insert using datetime(?, 'unixepoch')
■ ? is time_t
○ Query using datetime(timestamp, 'localtime')

16. SQL Debug
void* sqlite3_trace( sqlite3* db, trace_callback, void* udp);
// Register sql callback and call it every time before executing
void trace_callback( void* udp, const char* sql );
// udp means user data pointer

17. SQLite Busy Handle
● SQlite may be locked sometimes, solution:
○ sqlite3_busy_handle
■ More flexible, can add sleep() and retry times
○ sqlite3_busy_timeout
○ http://www.bubuko.com/infodetail-240892.html
○ http://www.360doc.
com/content/10/1214/12/87000_77984300.shtml

18. Relational Database
● MariaDB/MySQL/Percona
○ Multiple engines
■ MyISAM
● Table lock
■ InnoDB
● Row lock
● Transaction
● PostgreSQL
● SQLite

19. Relational Database
● Replication
○ For read
○ Master/Slave
● Sharding
○ For read/write
○ Do not rely on auto sharding

20. Reference
● http://stackoverflow.com/questions/1454188/how-can-i-analyse-a-sqlite-query-execution
● https://www.sqlite.org/docs.html
● http://www.cnblogs.com/likebeta/archive/2012/06/17/2552757.html