mySQL Workbench Error: Syntax Error, unexpected single quotes - php

Question

I was trying to make a SQL statement in PHP, to convert a string into a time(6). But I have tried everything, for the last 12 hours, and have not made an inch of progress. I have tried these statements, all yield the same error.
UPDATE scheduling SET start='03:42PM' WHERE activityid=2;
UPDATE scheduling SET start=CONVERT(TIME(6),'03:42PM');
INSERT INTO scheduling(start) VALUES (start=CONVERT(TIME(6),'03:42PM'));
INSERT INTO scheduling(start) VALUES (start=CONVERT(TIME(6),'03:42PM'));
INSERT INTO scheduling(start) VALUES (start=CONVERT(TIME(6),'15:42'));
The error is
Syntax Error: unexpected '03:42PM'(single quoted text)"
I do not know how to fix this, the table exists, and i have sucesfully got other info using statements like SELECT activityid=2 FROM xxxxxx.scheudling
I guess I have two questions, either answer would work.
In my PHP document, how would I convert a string I get in from an Android Studio volley to a date. (I get the variable correctly, with $start=$_Post("start"), so that works, but I cant convert it into a time. I looked online, and tried everything that looked like it work work.
Conversion through SQL Code, I already tried CAST and CONVERT, neither works. My start column is type TIME(6).

Answer 1

I recommend testing expressions using a SELECT statement.
Firstly, the MySQL CONVERT function arguments are flipped around backwards.
The syntax is CONVERT(expr,type)
And type is supplied as a keyword, not a string literal. For example:
SELECT CONVERT('235',SIGNED)
To convert to a TIME datatype
SELECT CONVERT( '15:42' ,TIME(6)) // => 15:42:00.000000
The 'PM' part of the string literal will be ignored.
SELECT CONVERT( '03:42PM' ,TIME(6)) // => 03:42:00.000000
We can use the STR_TO_DATE function to return a TIME value from a string that contains the AM/PM indicator
SELECT STR_TO_DATE( '03:42PM' ,'%h:%i%p')
And there's no need to cast that to TIME(6), we can do this:
UPDATE scheduling
SET start = STR_TO_DATE( '03:42PM' ,'%h:%i%p')
WHERE activityid = 2
The STR_TO_DATE function is documented here:
https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_str-to-date
The format patterns for STR_TO_DATE are documented here, under DATE_FORMAT:
https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_date-format
FOLLOWUP
Demonstration:
setup
USE test;
CREATE TABLE scheduling (activityid INT PRIMARY KEY, start TIME(6));
-- 0 row(s) affected
INSERT INTO scheduling (activityid) VALUES (2);
-- 1 row(s) affected
execute the update statement in the answer above
UPDATE scheduling SET start = STR_TO_DATE( '03:42PM' ,'%h:%i%p') WHERE activityid = 2 ;
-- 1 row(s) affected
results
SELECT * FROM scheduling WHERE activityid = 2;
-- activityid start
-- ---------- ---------------
-- 2 15:42:00.000000
SECOND FOLLOWUP
Use same sql_mode setting reported by OP:
SET ##sql_mode = 'ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION' ;
Test:
SELECT STR_TO_DATE( '03:42PM' ,'%h:%i%p')
returns
(NULL)
But this more complicated expression:
SELECT TIME(STR_TO_DATE(CONCAT(CURRENT_DATE(),' ', '03:42PM' ),'%Y-%m-%d %h:%i%p'))
returns
15:42:00
The more complicated expression is a workaround to avoid behavior imposed by the STRICT_TRANS_TABLES and NO_ZERO_DATE in the sql_mode.