QueryBuilderQueryBuilder is one of the most powerful features of TypeORM - it allows you to build SQL queries using elegant and convenient syntax, execute them and get automatically transformed entities.QueryBuilder:User:QueryBuilderQueryBuilder, you need to provide unique parameters in your WHERE expressions. This will not work::sheepId and :cowId instead of using :id twice for different parameters.QueryBuilderQuery Builder:QueryBuilder types available:SelectQueryBuilder - used to build and execute SELECT queries. Example:InsertQueryBuilder - used to build and execute INSERT queries. Example:UpdateQueryBuilder - used to build and execute UPDATE queries. Example:DeleteQueryBuilder - used to build and execute DELETE queries. Example:RelationQueryBuilder - used to build and execute relation-specific operations [TBD].QueryBuildergetOne:getOneOrFail will get a single result from the database, but if no result exists it will throw an EntityNotFoundError:getMany:getOne and getMany. But sometimes you need to select some specific data, let's say the sum of all user photos. This data is not an entity, it's called raw data. To get raw data, you use getRawOne and getRawMany. Examples:createQueryBuilder("user"). But what is "user"? It's just a regular SQL alias. We use aliases everywhere, except when we work with selected data.createQueryBuilder("user") is equivalent to:users is the table name, and user is an alias we assign to this table. Later we use this alias to access the table:user alias we assigned when we created a query builder.where("user.name = :name", { name: "Timber" }). What does { name: "Timber" } stand for? It's a parameter we used to prevent SQL injection. We could have written: where("user.name = '" + name + "'), however this is not safe, as it opens the code to SQL injections. The safe way is to use this special syntax: where("user.name = :name", { name: "Timber" }), where :name is a parameter name and the value is specified in an object: { name: "Timber" }.WHERE expressionWHERE expression is as easy as:AND into an existing WHERE expression:OR into an existing WHERE expression:IN query with the WHERE expression:WHERE expression into an existing WHERE using BracketsWHERE expression into an existing WHERE using NotBracketsAND and OR expressions as you need. If you use .where more than once you'll override all previous WHERE expressions.orWhere - if you use complex expressions with both AND and OR expressions, keep in mind that they are stacked without any pretences. Sometimes you'll need to create a where string instead, and avoid using orWhere.HAVING expressionHAVING expression is easy as:AND into an exist HAVING expression:OR into a exist HAVING expression:AND and OR expressions as you need. If you use .having more than once you'll override all previous HAVING expressions.ORDER BY expressionORDER BY expression is easy as:.orderBy more than once you'll override all previous ORDER BY expressions.DISTINCT ON expression (Postgres only)DISTINCT ON expression is easy as:GROUP BY expressionGROUP BY expression is easy as:addGroupBy:.groupBy more than once you'll override all previous GROUP BY expressions.LIMIT expressionLIMIT expression is easy as:take instead.OFFSET expressionOFFSET expression is easy as:skip instead.leftJoinAndSelect automatically loaded all of Timber's photos. The first argument is the relation you want to load and the second argument is an alias you assign to this relation's table. You can use this alias anywhere in query builder. For example, let's take all Timber's photos which aren't removed.INNER JOIN instead of LEFT JOIN just use innerJoinAndSelect instead:LEFT JOIN and INNER JOIN is that INNER JOIN won't return a user if it does not have any photos. LEFT JOIN will return you the user even if it doesn't have photos. To learn more about different join types, refer to the SQL documentation.leftJoin or innerJoin:profilePhoto to User entity and you can map any data into that property using QueryBuilder:user.profilePhoto. If you want to load and map a single entity use leftJoinAndMapOne. If you want to load and map multiple entities use leftJoinAndMapMany.QueryBuilder. To do so, use getSql:printSql:getOne and getMany. However, sometimes you need to select specific data, like the sum of all user photos. Such data is not a entity, it's called raw data. To get raw data, you use getRawOne and getRawMany. Examples:stream which returns you a stream. Streaming returns you raw data and you must handle entity transformation manually:take and skip may look like we are using limit and offset, but they aren't. limit and offset may not work as you expect once you have more complicated queries with joins or subqueries. Using take and skip will prevent those issues.