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How to combine parent table with multiple child tables?
Specifically to LEFT JOIN the parent table with each child: and then SELECT from the appropriate tables. Columns that are in both children tables can be combined with COALESCE (). The order of the expressions inside the function matter only if there are cases where an id appears in both childen.
How to display parent and child relationship in SQL?
Like someone posted earlier, it needs to be a recursive function. There can be multiple scenarios – One Parent to Multiple Child (Level 1 Hierarchy) Parent 1 has Child 1 Parent 1 has Child 2 Child to Multiple Child (Level 2 Hierarchy) And so on. My example has parent curve id and child curve id.
Can a parent have more than one child?
Effectively your code says: If a parent has two children, you get both; so the parent appears twice. If you want to only get the parent once you need to compromise; you can’t have both children.
When to create a parent-child relationship in SQL?
A parent-child relationship between two tables can be created only when there is a PRIMARY KEY in one table and FOREIGN KEY in another table. Syntax diagram – SQL JOIN of three tables Example: SQL JOIN – three or more tables Here is an example of SQL join three tables with conditions.
How to join recipes by ingredient ID in SQL?
SELECT r.name FROM RECIPES r JOIN RECIPEINGREDIENTS ri ON ri.recipe_id = r.id JOIN INGREDIENTS i ON i.id = ri.ingredient_id AND i.name IN (‘chocolate’, ‘cream’) GROUP BY r.name HAVING COUNT (DISTINCT i.name) = 2 The key point here is that the count must equal the number of ingredient names.
How to cheat in a Join-SQL query?
If you know for sure that the associations are unique (i.e. a single recipe can only have a single instance of each ingredient), then you can cheat a bit using a grouping subquery with a COUNT function and possibly speed it up (performance will depend on the DBMS):