#isnull

pandas.DataFrame、pandas.Seriesに欠損値（NaN）が含まれているか判定

要素ごと判定：isnull() or isna()

行・列ごとに判定： 　すべて欠損か：isnull().all() 　欠損を含むか：isnull().any() 　　※any(axis=1)で行チェック 　欠損値個数カウント： isnull().sum() 　　※sum(axis=1)で行チェック

A NULL value is a field with no value.It is very important to understand that the value of NULL is different from the zero value or a field containing spaces.   Syntax For Creating NULL Table CREATE TABLE Students( ID INT NOT NULL, NAME VARCHAR (225) NOT NULL, GENDER VARCHAR (225) , ADDRESS VARCHAR (225) , PRIMARY KEY (ID) ); Here, NOT NULL means that the column must accept the specified value of…

SQL Coalesce Function and NULL

Knowing when to use the SQL COALESCE function is a lifesaver when you’re dealing with NULL.

As you know, NULL is a tricky concept, and it seem what ever NULL “touches” in an expression, it renders the result NULL. So, when you’re dealing with NULL, how can you break out of the cycle? That is, how can you display another value instead?

This is where SQL COALESCE comes into play. With this…

SQL Union without using Set Operations

  In this puzzle, we’re going to learn how to write a SQL UNION without using Set Operations.  Set operations allow us to compare rows from two or more tables to arrive at a result.   For several classes of problems, it is much easier to use a set operation, than join data.  But can we do without a SQL UNION?

Yet a great way to know and understand SQL is to explore alternative methods.  Today…

It is OK its NULL only TIP #103

  We always take NULL very lightly. Like if we are designing database then whether it is necessary or not we allow the data field to accept null.We think it will not affect anything.

Actually , at some point this is not always true.

According to Microsoft NULL is an Unknown value. It is not EMPTY & ZERO. It is just unknown.

Now according to my experience NULL is very sensitive and should be…

Find first not null value from different columns TIP # 47

  Problem:

Sometimes, it might be possible that we need not null value only from particular columns and if all column have null value then we provide a default value.

Lets understand this by a general and very interesting example

suppose a friend come to your house and you want to give him a treat then you check your first column or we can say first option “Is there any thing to eat ?” if that…

Sql server interview questions and answers: