sql - Check if a table has X amount of records -

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i have script connects database , inserts data based on form selections 

function(tx) {             ensuretableexists(tx);             var firstname = firstnamebox.value;             var playingposition = playingpositionbox.value;             var sql = 'insert yellows (firstname, playingposition) values ("' + firstname + '","' + playingposition + '")';             tx.executesql(sql);         },

what best method search if table has 5 entries. if database has 5 entries reject insert statement , inform user there no space.


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