SQLite
SQLite is a relational database management system (RDBMS) contained in a C library. In contrast to many other database management systems, SQLite is not a client–server database engine. Rather, it is embedded into the end program.
SQLite is ACID-compliant and implements most of the SQL standard, generally following PostgreSQL syntax. However, SQLite uses a dynamically and weakly typed SQL syntax that does not guarantee the domain integrity.[7] This means that one can, for example, insert a string into a column defined as an integer. SQLite will attempt to convert data between formats where appropriate, the string "123" into an integer in this case, but does not guarantee such conversions and will store the data as-is if such a conversion is not possible.
SQLite is a popular choice as embedded database software for local/client storage in application software such as web browsers. It is arguably the most widely deployed database engine, as it is used today by several widespread browsers, operating systems, and embedded systems (such as mobile phones), among others.
Operators and statements⚑
Upsert statements⚑
UPSERT is a special syntax addition to INSERT that causes the INSERT to behave as an UPDATE or a no-op if the INSERT would violate a uniqueness constraint. UPSERT is not standard SQL. UPSERT in SQLite follows the syntax established by PostgreSQL.
The syntax that occurs in between the "ON CONFLICT" and "DO" keywords is called the "conflict target". The conflict target specifies a specific uniqueness constraint that will trigger the upsert. The conflict target is required for DO UPDATE upserts, but is optional for DO NOTHING. When the conflict target is omitted, the upsert behavior is triggered by a violation of any uniqueness constraint on the table of the INSERT.
If the insert operation would cause the uniqueness constraint identified by the conflict-target clause to fail, then the insert is omitted and either the DO NOTHING or DO UPDATE operation is performed instead. In the case of a multi-row insert, this decision is made separately for each row of the insert.
The special UPSERT processing happens only for uniqueness constraint on the table that is receiving the INSERT. A "uniqueness constraint" is an explicit UNIQUE or PRIMARY KEY constraint within the CREATE TABLE statement, or a unique index. UPSERT does not intervene for failed NOT NULL or foreign key constraints or for constraints that are implemented using triggers.
Column names in the expressions of a DO UPDATE refer to the original unchanged value of the column, before the attempted INSERT. To use the value that would have been inserted had the constraint not failed, add the special "excluded." table qualifier to the column name.
CREATE TABLE phonebook2(
name TEXT PRIMARY KEY,
phonenumber TEXT,
validDate DATE
);
INSERT INTO phonebook2(name,phonenumber,validDate)
VALUES('Alice','704-555-1212','2018-05-08')
ON CONFLICT(name) DO UPDATE SET
phonenumber=excluded.phonenumber,
validDate=excluded.validDate
REGEXP⚑
The REGEXP operator is a special syntax for the regexp() user function. No regexp() user function is defined by default and so use of the REGEXP operator will normally result in an error message. If an application-defined SQL function named regexp is added at run-time, then the X REGEXP Y operator will be implemented as a call to regexp(Y,X). If you're using sqlite3, you can check how to create the regexp function.
Snippets⚑
Order by a column descending⚑
SELECT
select_list
FROM
table
ORDER BY
column_1 ASC,
column_2 DESC;
Import a table from another database⚑
If you have an SQLite databases named database1 with a table t1 and database2 with a table t2 and want to import table t2 from database2 into database1. You need to open database1 with litecli:
litecli database1
Attach the other database with the command:
ATTACH 'database2file' AS db2;
Then create the table t2, and copy the data over with:
INSERT INTO t2 SELECT * FROM db2.t2;
Get the columns of a database⚑
PRAGMA table_info(table_name);
Troubleshooting⚑
[Integer autoincrement not⚑
working](https://stackoverflow.com/questions/16832401/sqlite-auto-increment-not-working)
Rename the column type from INT to INTEGER and it starts working.
From this:
CREATE TABLE IF NOT EXISTS foo (id INT PRIMARY KEY, bar INT)
to this:
CREATE TABLE IF NOT EXISTS foo (id INTEGER PRIMARY KEY, bar INT)
