NodeJS 和 MySQL：SQL 语法错误导致 UnhandledPromiseRejectionWarning

Question

I am querying a database using NodeJS and MySQL and async functions. I have the following query in my async function:

async function get_data(sample) {

let pool, con;
try {
    pool = await mysql.createPool(config.databaseOptions);
    con = await pool.getConnection();
} catch (err) {
    console.error('Could not connect to database');
    return false;
}

var qry = "SELECT " +
"   t1.sample_id, t1.v_id, t1.s_type as type, t1.sf, " +
"   t1.ef, CONCAT(t1.chr_bkpt1, ':', t1.pos_bkpt1) as b1, " +
"   CONCAT(t1.chr_bkpt2, ':', t1.pos_bkpt2) as b2, " +
"   t1.sge, t1.ege, t1.pscore as som_score, " +
"   t1.wgs, t1.frame, t1.platform, t1.rconf, t1.report, " +
"   t1.target, t1.pclass, t1.evidence, t2.summary, t3.comments " +
"   FROM " +
"   ( " +
"       SELECT s.* " +
"       FROM sample_som s " +
"       WHERE sample_id=? " +
"   ) as t1 " +
"   LEFT JOIN " +
"   ( " +
"       SELECT v_id, c.sample_id, " +
"       CONCAT(c.sample_id,'(',e.disease_type,'): ',c.cur_summary) as summary " +
"       FROM samples e " +
"       LEFT JOIN sample_som c " +
"       ON e.sample_id=c.sample_id " +
"       WHERE c.cur_summary is not null " +
"       AND c.sample_id=? " +
"   ) as t2 " +
"   ON t1.v_id=t2.v_id " +
"   LEFT JOIN ( " +
"       SELECT v_id, c.sample_id, " +
"       CONCAT(c.sample_id,'(',e.disease_type,'): ',c.comments) as comments " +
"       FROM samples e " +
"       LEFT JOIN sample_som c " +
"       ON e.sample_id=c.sample_id " +
"       WHERE c.comments is not null " +
"       AND c.sample_id=? " +
"   ) as t3 " +
"   ON t1.v_id=t3.v_id " +
"   ORDER BY t1.v_id";

const [rows,fields] = await con.query(qry, sample);
await con.release();
return rows;
}

However, I am getting the following error when I run the server:

UnhandledPromiseRejectionWarning: Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?)    as t2    ON t1.v_id=t2.v_id    LEFT JOIN (        SELECT v_id' at line 1

I am not sure why I am getting this error and how to resolve this. Any insights are appreciated.

Answer 1

tl;dr Your sample array isn't long enough.

This is one of those cases where a careful reading of the error message will identify your problem. MySQL could not parse your query. The first character it did not understand was your second ? placeholder.

You have three ? placeholders in your query, and you have offered the sample parameter in your call to con.query(qry, sample) . That parameter must be an array with the same number of elements as you have placeholders.

You have not provided a catch handler around your query operation, so node is throwing the UnhandledPromiseRejectionWarning when your query fails. Pro tip : always catch and handle errors from DBMSs.

You can use multiline string constants to hold long queries. For example

const qry = `
SELECT a,b
  FROM c
 WHERE id = ?
 ORDER BY b;`;

Pro tip: These are much easier to read and edit than the style you used in your example, especially for complex queries such as yours.