UPPERCASE Constraint in SQL

What will be the query to add UPPERCASE Constraint to a column of pre-existing table? The question demands to ensure that the entries are in UPPERCASE.

You could use a CHECK constraint to enforce that the column always contains uppercase values.

-- as new table
CREATE TABLE t1(c1 VARCHAR(200) CONSTRAINT c1_upper CHECK (BINARY UPPER(c1) = BINARY c1));
INSERT INTO t1(c1) VALUES ('a');
INSERT INTO t1(c1) VALUES ('A');
SELECT * FROM t1;

-- altering existing table
CREATE TABLE t2 (c2 VARCHAR(200) NOT NULL);
ALTER TABLE t2 ADD CONSTRAINT c2_upper CHECK (BINARY c2 = BINARY UPPER(c2));
INSERT INTO t2(c2) VALUES ('a');
INSERT INTO t2(c2) VALUES ('A');
SELECT * FROM t2;

SQL Fiddle: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=a4d4e277ea6993d7b66a3b2f4871a320

Older versions of MySQL don’t have check constraints. You can work around this by doing DML against a checked view. This works in version 5.5.

CREATE TABLE t1(c1 VARCHAR(200));
CREATE VIEW v1 AS SELECT * FROM t1 WHERE BINARY c1 = BINARY UPPER(c1) WITH CHECK OPTION;
INSERT INTO v1(c1) VALUES ('a');
-- fails
INSERT INTO v1(c1) VALUES ('A');
-- succeeds

SQL fiddle: https://dbfiddle.uk/?rdbms=mysql_5.5&fiddle=7416cfbbbbbd1161d48785dd384d5d30