Evaluate true/false on string saved expression

dimitrysdimitrys Registered User

Hi,
if a have a stored expressions in a column, can I evaluate it to true or false?

for example,
I have a column with values like:
exp (column name)
1=1
1=1 and 'a'<>'b'

and want to get back:
exp eval_result
1=1 true
1=1 and 'a'<>'b' true
1=1 and 'a'='l' true

is it possible?

Answers

  • Jim_KnicelyJim_Knicely Administrator, Moderator, Employee, Registered User, VerticaExpert
    edited May 22

    My immediate thought is to generate SQL statements to evaluate the expressions...

    Example:

    dbadmin=> SELECT * FROM boolean_operators;
           exp
    ------------------
     1=1
     1=1 and 'a'<>'b'
     1=1 and 'a'='l'
    (3 rows)
    
    dbadmin=> \! vsql -Atc "SELECT 'SELECT ''' || REPLACE(exp, CHR(39), CHR(39) || CHR(39)) || ''' exp, (SELECT ' || exp || ') eval_resuls;' FROM boolean_operators;" | vsql
     exp | eval_resuls
    -----+-------------
     1=1 | t
    (1 row)
    
           exp        | eval_resuls
    ------------------+-------------
     1=1 and 'a'<>'b' | t
    (1 row)
    
           exp       | eval_resuls
    -----------------+-------------
     1=1 and 'a'='l' | f
    (1 row)
    

    Or this:

    dbadmin=> \! vsql -Atc "SELECT 'SELECT ''' || REPLACE(exp, CHR(39), CHR(39) || CHR(39)) || ''' exp, (SELECT ' || exp || ') eval_resuls ' || DECODE(LEAD(exp) OVER (ORDER BY 1), NULL, '', 'UNION ALL') FROM boolean_operators;" | vsql
           exp        | eval_resuls
    ------------------+-------------
     1=1 and 'a'='l'  | f
     1=1              | t
     1=1 and 'a'<>'b' | t
    (3 rows)
    

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