query return null in bash for psql - bash

Question

I am tring to get the count for the records in a certain table in bash scripts but the $num is null when returned (should be a number). And the query is correct when I directly run in pgadmin that I can get the number of rows. Any one know what is wrong?
declare -a ROW=($(psql \
-X \
-U $DB_USER \
-h $DB_HOST \
-d $DB_NAME \
-p $DB_PORT \
--set ON_ERROR_STOP=on \
--no-align \
-t \
--field-separator ' ' \
--quiet \
-c "SELECT count(*) as num
FROM table_test)")
)
echo "num_error: $num here"
if [[ $num == 0 ]]; then
echo "no error occur within the past 1 hour"
elif [[ $num == '' ]]; then
echo "return nothing"
else echo "$num"
fi

Answer 1

SQL aliases don't become shell variables, so using AS num in the query will not set $num in the shell.
The output of the query is being put in the ROW array, so you can get the value you want from ${ROW[0]}. There's also no need to use an array if the query just returns a single value. So you could do:
num=$(psql \
-X \
-U $DB_USER \
-h $DB_HOST \
-d $DB_NAME \
-p $DB_PORT \
--set ON_ERROR_STOP=on \
--no-align \
-t \
--field-separator ' ' \
--quiet \
-c "SELECT count(*)
FROM table_test)")
)