WITH Letters AS (
    Select 'a' AS c UNION ALL
    Select 'b' UNION ALL
    Select 'c' UNION ALL
    Select 'd' UNION ALL
    Select 'e' UNION ALL
    Select 'f' UNION ALL
    Select 'g' UNION ALL
    Select 'h' UNION ALL
    Select 'i' UNION ALL
    Select 'j' UNION ALL
    Select 'k' UNION ALL
    Select 'l' UNION ALL
    Select 'm' UNION ALL
    Select 'n' UNION ALL
    Select 'o' UNION ALL
    Select 'p' UNION ALL
    Select 'q' UNION ALL
    Select 'r' UNION ALL
    Select 's' UNION ALL
    Select 't' UNION ALL
    Select 'u' UNION ALL
    Select 'v' UNION ALL
    Select 'w' UNION ALL
    Select 'x' UNION ALL
    Select 'y' UNION ALL
    Select 'z'
)
Insert INTO DomainNameTB (DomainName)
Select L1.c + L2.c + '.com'
FROM Letters L1
CROSS JOIN Letters L2;
GO

Insert INTO DomainNameTB (DomainName)
Select
    L1.c + L2.c + L3.c + '.com'
FROM Letters L1
CROSS JOIN Letters L2
CROSS JOIN Letters L3;