If you need a refresher on the SQL JOIN syntax, check out this great SQL JOIN Cheat Sheet. ON s.teacher_first_name = t.first_name AND s.teacher_last_name = t.last_name SELECT s.first_name, s.last_name, s.teacher_first_name, s.teacher_last_name, t.education AS teacher_education As long as we don't have teachers with identical full names, we can safely join these tables by these two columns. However, we do have the teacher's first and last names in both tables. Unfortunately, we don't have the teacher ID column in the students table. For this, we need to combine the information from the tables students and teachers. In our first example, we want to know the education level of the teacher for each student. It’s time for a couple of SQL queries! Example 1: SQL JOIN by Two Columns However, even with the data stored like this, we can join the tables as long as each table has a set of columns that uniquely identifies each record. Typically, the students table would include foreign keys like the teacher ID and the class ID instead of detailed information about the corresponding teachers and classes. You might notice our database is not perfectly organized. classes, where we have information about each class, such as the name of the kindergarten, the class, the graduation year, and the name of the classroom.teachers, where we have the name and the education level of each teacher.students, where we have information about each student, such as the name, the kindergarten he or she attended, the class, the graduation year, and the teacher.In our database, we have the following tables: Let’s imagine we run a network of kindergartens. Let’s see some examples to understand how this works in practice. The explanations are based on real-world examples that resemble problems you'll meet daily. ![]() ![]() It contains over 90 exercises that cover different JOIN topics: joining multiple tables, joining by multiple columns, different JOIN types ( LEFT JOIN, RIGHT JOIN, FULL JOIN), or joining table with itself. The best way to practice SQL JOINs is our interactive SQL JOINs course. In situations like these, you may need to use multiple columns to join tables – e.g., the first and the last names, or the order number and the year if the order numbering restarts each year. Or the tables you want to join may not have just one common column to use for joining. For example, you may encounter cases in which there is no one column in the table that uniquely identifies the rows. Joining tables by just one column does not work in some scenarios. In this article, I’ll discuss why you would want to join tables by multiple columns and how to do this in SQL. ![]() However, it is also often the case that you need to join tables by two or more columns. Most often, you’ll be joining tables based on a primary key from one table and a foreign key from another table. In the above example, you will get records of not matching with Brazil (BRA), the United States of America (USA), and Canada(CAN).The SQL JOIN is an important tool for combining information from several tables. How to use multiple NOT LIKE conditions select country_cde, date, name, age In the above example, I did filter records of matching with either Brazil (BRA), the United States of America (USA), and Canada(CAN). select column1, column2, column3įrom my_table Real-life example with multiple Like conditionsīelow example is to get records from TRAVEL-DET table (travel details table). select column1, column2, column3įrom my_table How to give Multiple Like Conditionsīelow example says, general syntax of usage of multiple like conditions in Where clause. ![]() Below is the simple SQL to give Like condition in Where clause.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |