Not sure how exactly DataGrip works for prompting input, but a CTE should allow you to declare the constant once:
WITH x AS (SELECT :myinput AS alias5)
SELECT fld1 as alias1, fld2 as alias2, fld3 as alias3, fld4 as alias4, alias5 FROM table1, x WHERE condition1
SELECT fld1 as alias1, fld2 as alias2, fld3 as alias3, fld4 as alias4, alias5 FROM table2, x WHERE condition2
SELECT fld1 as alias1, fld2 as alias2, fld3 as alias3, fld4 as alias4, alias5 FROM table3, x WHERE condition3
SELECT fld1 as alias1, fld2 as alias2, fld3 as alias3, fld4 as alias4, alias5 FROM table4, x WHERE condition4
Greg