Maybe this can help you, I'm now on mobile dev section, but I got a question about SQL, actually what you should know about some SQL here is

- What is DBMS

- MYSQL

- Query

- Join table

- data types

- SQL structure

- sql command

This is my question, yes you should know about sql and how to implement it in application or web (live performance)

I'm currently still a student, but I'm a freelancer, sometimes I'm also interviewed to convince the client that I can. For that I will share about some of the questions they asked. You need to know that I was not interviewed in sql only but with coding, for example how to make a UI display, backend, data processing and output data and finally SEO and Security such as SEO, I can only answer about web and SQL, basic SEO, Security basic, I will describe it

- What is a DBMS?

- What is the query?

- Case sql query ex : join table, select, where, anything

- SQL structure

- Primary key

- Sql data types

- Case

Create databases, queries, and join tables and describe what you create

Coding

- Php fundamental

- Laravel

- UI like css or bootstrap

- Making simple web app

- Web testing

- Basic SEO

- Security like validation, filtering, session

This site helps me to get an overiview about SQL

https://www.guru99.com/sql-interview-questions-answers.html 

Oh I forgot, you must now about relation like constraint, restrict, cascade, on delete and foreign key. Maybe this help you because in SQL many relation, FK and how you make a query