IF EXISTS(SELECT 1 FROM TABLE_NAME WHERE COL_A = 'A' AND COL_B = 'B' AND COL_C = 10)
    BEGIN
        UPDATE TABLE_NAME
        SET COL_D = 'D' COL_E = 'E'
        WHERE COL_A = 'A' AND COL_B = 'B' AND COL_C = 10 AND COL_C > 15
    END
ELSE
    BEGIN
        INSERT INTO TABLE_NAME
        (COL_A, COL_B, COL_C, COL_D, COL_E)
        VALUES
        ('A', 'B', 10, 'D', 'E')
    END

IF EXISTS(SELECT 1 FROM TABLE_NAME WHERE COL_A = ? AND COL_B = ? AND COL_C = ?)
    BEGIN
        UPDATE TABLE_NAME
        SET COL_D = ? COL_E = ?
        WHERE COL_A = ? AND COL_B = ? AND COL_C = ? AND COL_C > 15
    END
ELSE
    BEGIN
        INSERT INTO TABLE_NAME
        (COL_A, COL_B, COL_C, COL_D, COL_E)
        VALUES
        (?, ?, ?, ?, ?)
    END