Skip to main content

SQL WHERE EXISTS Statement with Example

SQL WHERE EXISTS Statement

  • WHERE EXISTS tests for the existence of any records in a subquery.
  • EXISTS returns true if the subquery returns one or more records.
  • EXISTS is commonly used with correlated subqueries.

The SQL EXISTS syntax

The general syntax is:
  1. SELECT column-names FROM table-name WHERE EXISTS (SELECT column-name FROM table-name WHERE condition)

SQL EXISTS Example

Comments

Popular posts from this blog

important question on Entity Relationship Model(ER Model)

5)A university registrar’s office maintains data about the following entities: (a) courses, including number, title, credits, syllabus, and prerequisites; (b) course offerings, including course number, year, semester, section number, instructor(s), timings, and classroom; (c) students, including student-id, name, and program; and (d) instructors, including identification number, name, department, and title. Further, the enrollment of students in courses and grades awarded to students in each course they are enrolled for must be appropriately modeled. Construct an E-R diagram for the registrar’s office. Document all assumptions that you make about the mapping constraints. Answer:   In the answer given here, the main entity sets are student, course, course-offering, and instructor. The entity set course-offering is a weak entity set dependent on course. The assumptions made are : a class meets only at one particular place and time. This E - R diagram cannot model a c...

how to Install Numpy, Pandas and matplotlib on ubuntu 18.04 and Linux Mint

Install Python, NumPy,Matplotlib for Python 3 on Ubuntu 18.04, Linux Mint, Debian Linux. This is a short article about installing Numpy, Pandas , Matplotlib, Python3 on the latest Ubuntu 18.04 LTS, Linux Mint, Debian Linux which comes with Python 3.6.5. Let’s start by making sure we have an updated system: 1 sudo apt update 2 sudo apt upgrade Now, let’s install NumPy, Pandas,Matplotlib : sudo apt-get install python-pip sudo pip install numpy sudo pip install pandas sudo pip install matplotlib Test numpy : Open up a Terminal in Your Linux Operating System by running the following: python3 At the Terminal, type the following: >>> import numpy as np >>> np.__version__ '1.13.3'   Test Pandas : Open up a Terminal in Your Linux Operating System by running the following: python3 At the Terminal, type the following: >>> import pandas as pd >>> pd.__version__ '0.22.0'   Test Matpl...

Kleene Star Closure , Kleen Plus Operation and Recursive definition of languages

Kleene Star Closure Given Σ, then the Kleene Star Closure of the alphabet Σ, denoted by Σ * , is the collection of all strings defined over Σ, including Λ. It is to be noted that Kleene Star Closure can be defined over any set of strings. Examples If Σ = {x} Then Σ * = {Λ, x, xx, xxx, xxxx, ....} If Σ = {0,1} Then Σ * = {Λ, 0, 1, 00, 01, 10, 11, ....} If Σ = {aaB, c} Then Σ * = {Λ, aaB, c, aaBaaB, aaBc, caaB, cc, ....} Note Languages generated by Kleene Star Closure of set of strings, are infinite languages. (By infinite language, it is supposed that the language contains infinite many words, each of finite length). Kleen PLUS Operation ( + ) Kleen Plus Operation is same as Kleene Star Closure except that it does not generate Λ (null string), automatically. Example If Σ = {0,1} Then Σ + = {0, 1, 00, 01, 10, 11, ....} If Σ = {aab, c} Then Σ + = {aab, c, aabaab, aabc, caab, cc, ....} Remark It is to be noted that Kleene Star can also be operated on any str...