How to INSERT INTO table(column) VALUES(value) WHERE column2 = value - sql

Question

I am working on a Time Clock program but I am having trouble with this query:
INSERT INTO users(time_in) VALUES($2) WHERE username = $1
Table:
CREATE TABLE users (
id SERIAL PRIMARY KEY NOT NULL,
username VARCHAR(50) NOT NULL,
password VARCHAR(255) NOT NULL,
email VARCHAR(255) NOT NULL,
time_json VARCHAR,
time_in VARCHAR
);
Here is the error that I am getting:
error: syntax error at or near "time_in"
at Connection.parseE (\...\node_modules\pg\lib\connection.js:606:11)
at Connection.parseMessage (\...\node_modules\pg\lib\connection.js:403:19)
at TLSSocket.<anonymous> (\...\node_modules\pg\lib\connection.js:123:22)
at TLSSocket.emit (events.js:210:5)
at addChunk (_stream_readable.js:308:12)
at readableAddChunk (_stream_readable.js:289:11)
at TLSSocket.Readable.push (_stream_readable.js:223:10)
at TLSWrap.onStreamRead (internal/stream_base_commons.js:182:23) {
name: 'error',
length: 95,
severity: 'ERROR',
code: '42601',
detail: undefined,
hint: undefined,
position: '8',
internalPosition: undefined,
internalQuery: undefined,
where: undefined,
schema: undefined,
table: undefined,
column: undefined,
dataType: undefined,
constraint: undefined,
file: 'scan.l',
line: '1134',
routine: 'scanner_yyerror'}
Code for the function I am working on:
function postTimeIn(user, callback) {
const timeIn = getTime();
params = [user, timeIn];
const sql = 'INSERT INTO users(time_in) VALUES($2) WHERE username = $1';
pool.query(sql, params, function (err, result) { ...

Answer 1

The WHERE clause would make sense with an UPDATE:
UPDATE users
SET time_in = $2
WHERE username = $1;
Is that what you really want?
username should be defined UNIQUE for this - and probably in any case.
time_json should probably be type json or jsonb. time_in should probably be timestamptz.
An INSERT would not make any sense (apart from the invalid syntax), as you would have to fill in all NOT NULL columns without column default at the same time:
username VARCHAR(50) NOT NULL,
password VARCHAR(255) NOT NULL,
email VARCHAR(255) NOT NULL,

Answer 2

The problem is that you are trying to insert a record with a where condition. You can only use a where condition only as a filter when you are inserting values selected from another table
like.
INSERT INTO table(column1,column2,...)
SELECT column1,column2,...
FROM another_table
WHERE condition;
In your instant you should do an update as suggested above because you are changing the attribute value of an already existing record.