MySQL 8.0

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CREATE TABLE Tbl(num float(2,1))
INSERT INTO Tbl(num) VALUES(0.1)
SELECT MAX(IF(TRUE, num, 0))   FROM Tbl

MAX(IF(TRUE, num, 0))

0.1

CREATE TABLE Tbl2(num float)
INSERT INTO Tbl2(num) VALUES(0.1)
SELECT ROUND(MAX(IF(TRUE, num, 0)),1)   FROM Tbl2

ROUND(MAX(IF(TRUE, num, 0)),1)

0.1