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Found 3 results

  1. I'm working on this session, and it shows if I'd like to test NULL value, I'll need to use below syntax: However, I'd like to know what if I have no idea which column(s) has(have) NULL value? How should I make a query to look for ANY record that includes NULL value without writing specific column_name?
  2. Hi There, I have two questions about SQL syntax, the first one is about "SELECT DISTINCT" and the other is "NOT". Question 1: For example, "Customers" table has fields including CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country. From my understanding, if my SQL statement is SELECT DISTINCT Country FROM Customers; then it will show the list of unique countries. However, I'd like to know what does it mean if my SQL statement is SELECT DISTINCT Country, City, CustomerName FROM Customers; ? Why I don't have to write SELECT DISTINCT Country, DISTINCT City, DISTINCT CustomerName? You may refer to this session: https://www.w3schools.com/sql/sql_distinct.asp Question 2: I'm working on the session, and there's an example as below: I understand that this example would like to exclude BOTH Country = "Germany" and Country = "USA", but I don't understand why using the operator [AND] instead of [OR]? Doesn't [AND] represent the intersection while [OR] mean union? So, if I want to exclude BOTH "Germany" and "USA", why I can't use [OR] as the operator in this example?
  3. Hi All, I've recently encountered this line of javaScript code. return (controlName.attr('type') || controlName[0].tagName).toLowerCase(); I haven't ever seen this structure before. Can anybody explain it to me. I am confused as to what the or ( || ) is doing. One of the two strings ( either controlName.attr('type') or controlName[0].tagName) is being processed by the toLowerCase() library function. But I am unsure of what the procedure is. If the object has both a type attribute and a tag name then what is actually being returned? Thanks PMingione
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