SQLite table constraint – unique on multiple columns

compound-keysqliteunique-constraint

I can find syntax "charts" on this on the SQLite website, but no examples and my code is crashing. I have other tables with unique constraints on a single column, but I want to add a constraint to the table on two columns. This is what I have that is causing an SQLiteException with the message "syntax error".

CREATE TABLE name (column defs) 
UNIQUE (col_name1, col_name2) ON CONFLICT REPLACE

I'm doing this based on the following:

table-constraint

To be clear, the documentation on the link I provided says that CONTSTRAINT name should come before my constraint definition.

Something that may lead to the solution though is that whatever follows my parenthesized column definitions is what the debugger complains about.

If I put

...last_column_name last_col_datatype) CONSTRAINT ...

the error is near "CONSTRAINT": syntax error

If I put

...last_column_name last_col_datatype) UNIQUE ...

the error is near "UNIQUE": syntax error

Best Answer

Put the UNIQUE declaration within the column definition section; working example:

CREATE TABLE a (
    i INT,
    j INT,
    UNIQUE(i, j) ON CONFLICT REPLACE
);

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Sql – How to list the tables in a SQLite database file that was opened with ATTACH

There are a few steps to see the tables in an SQLite database:

List the tables in your database:
```
.tables
```
List how the table looks:
```
.schema tablename
```
Print the entire table:
```
SELECT * FROM tablename;
```
List all of the available SQLite prompt commands:
```
.help
```

SQLite – UPSERT not INSERT or REPLACE

Assuming three columns in the table: ID, NAME, ROLE

BAD: This will insert or replace all columns with new values for ID=1:

INSERT OR REPLACE INTO Employee (id, name, role) 
  VALUES (1, 'John Foo', 'CEO');

BAD: This will insert or replace 2 of the columns... the NAME column will be set to NULL or the default value:

INSERT OR REPLACE INTO Employee (id, role) 
  VALUES (1, 'code monkey');

GOOD: Use SQLite On conflict clause UPSERT support in SQLite! UPSERT syntax was added to SQLite with version 3.24.0!

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.

GOOD but tedious: This will update 2 of the columns. When ID=1 exists, the NAME will be unaffected. When ID=1 does not exist, the name will be the default (NULL).

INSERT OR REPLACE INTO Employee (id, role, name) 
  VALUES (  1, 
            'code monkey',
            (SELECT name FROM Employee WHERE id = 1)
          );

This will update 2 of the columns. When ID=1 exists, the ROLE will be unaffected. When ID=1 does not exist, the role will be set to 'Benchwarmer' instead of the default value.

INSERT OR REPLACE INTO Employee (id, name, role) 
  VALUES (  1, 
            'Susan Bar',
            COALESCE((SELECT role FROM Employee WHERE id = 1), 'Benchwarmer')
          );

Best Answer

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Sql – How to list the tables in a SQLite database file that was opened with ATTACH

SQLite – UPSERT *not* INSERT or REPLACE

Related Topic

SQLite – UPSERT not INSERT or REPLACE