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Conditional constraint unique

I have the following table

create table use_flags3 (
    id INTEGER,
    flag_name VARCHAR NOT NULL,        
    flag_description VARCHAR NOT NULL,
    flag_type_id INTEGER NOT NULL,
    package_id INTEGER,
    FOREIGN KEY (flag_type_id) REFERENCES use_flags_types(id),
    FOREIGN KEY (package_id) REFERENCES packages(id),
    PRIMARY KEY (id)
);

I need a column flag_nameto be unique only when flag_type_id is 1. I tried to achieve this with the following restriction

CONSTRAINT idx1_chk CHECK (
    flag_type_id in (select id from use_flags_types where flag_type="local") or
    flag_type_id in (select id from use_flags_types where flag_type="expand") or
    flag_type_id in (select id from use_flags_types where flag_type="expand_hidden") or
    (
         flag_type_id in (select id from use_flags_types where flag_type="global") and
         flag_name not in (select flag_name from use_flags)
    )
)

sqlite says that "subqueries are not allowed in CHECK constraints." I can replace

flag_type_id in (select id from use_flags_types where flag_type="local")

with

flag_type_id = ${ID_HERE} -- id from `select id from use_flags_types where flag_type="local"`

but I can’t do the same trick for the second part of the last part of the restriction

flag_name not in (select flag_name from use_flags)

Is there a chance to do what I originally wanted in one table (I really would not want to split this data into 2 (+) tables)?

// the description of hope is pretty clear

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1 answer

If you have a complex limitation, you should use triggers:

http://sqlfiddle.com/#!7/2094c

CREATE TABLE use_flags3 (
    id INTEGER,
    flag_name VARCHAR NOT NULL,
    flag_description VARCHAR NOT NULL,
    flag_type_id INTEGER NOT NULL,
    package_id INTEGER,
    FOREIGN KEY (flag_type_id) REFERENCES use_flags_types(id),
    FOREIGN KEY (package_id) REFERENCES packages(id),
    PRIMARY KEY (id)
);

/* TRIGGER BEFORE UPDATE version omitted */

CREATE TRIGGER fake_unique
BEFORE INSERT ON use_flags3
FOR EACH ROW
WHEN (
    EXISTS (SELECT NULL
            FROM use_flags_types
            WHERE flag_type IN( "local", "expand", "expand_hidden")
              AND flag_type_id = id
           )
    OR (
         EXISTS (SELECT NULL
                 FROM use_flags_types
                 WHERE flag_type="global"
                 AND flag_type_id = id)
         AND flag_name NOT IN (SELECT flag_name FROM use_flags)
    )
)
BEGIN
  SELECT RAISE( ABORT, 'duplicate rows' );
END;
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