I have developed a query, and in the results for the first three columns I get NULL. How can I replace it with 0?
select a,b,null,null from table1 union select null,null,c,d from table2 union select null,null,null,null,e,f from table3.
Postgres is the database Can I use a NULL value for a IN clause? example: … I want to limit to these four values. I have tried the above statement and it doesn't work...
What is the difference between … and … and why does the latter not work?
Then in the second table I have select ..., null as opt from... I know that I could have an empty string with '' as opt however, I don't want an empty string, I really do need it to be null.
How can I run a MySQL query that selects everything that is not null? It would be something like … Do I just remove the all and go..?
union all select null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null
Note: A NULL value is different from a zero value or a field that contains spaces.
SQL’s NULL indicates absent data. NULL propagates through expressions and needs distinct
Null (or NULL) is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd...