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How do you know when to use left join or right join?

How do you know when to use left join or right join?

The main difference between these joins is the inclusion of non-matched rows. The LEFT JOIN includes all records from the left side and matched rows from the right table, whereas RIGHT JOIN returns all rows from the right side and unmatched rows from the left table.

How do I know which join to use in SQL?

Different Types of SQL JOINs

  1. (INNER) JOIN : Returns records that have matching values in both tables.
  2. LEFT (OUTER) JOIN : Returns all records from the left table, and the matched records from the right table.
  3. RIGHT (OUTER) JOIN : Returns all records from the right table, and the matched records from the left table.

Which join should I use?

Generally, we use INNER JOIN when we want to select only rows that match an ON condition. We use a LEFT JOIN when we want every row from the first table, regardless of whether there is a matching row from the second table. This is similar to saying, “Return all the data from the first table no matter what.

IS LEFT JOIN faster than right join?

A LEFT JOIN is absolutely not faster than an INNER JOIN . In fact, it’s slower; by definition, an outer join ( LEFT JOIN or RIGHT JOIN ) has to do all the work of an INNER JOIN plus the extra work of null-extending the results.

Which join is faster in Hana?

Join Left outer join

Should you ever use a right join?

The only reason I can think of to use RIGHT OUTER JOIN is to try to make your SQL more self-documenting. You might possibly want to use left joins for queries that have null rows in the dependent (many) side of one-to-many relationships and right joins on those queries that generate null rows in the independent side.

Whats the point of right join?

The RIGHT JOIN keyword returns all records from the right table (table2), and the matching records from the left table (table1). The result is 0 records from the left side, if there is no match.

Why do we need right join?

Right joins make it easier for programming languages to generate proper SQL in a performant manner, especially when user behavior can dictate the join type. Rather than reorganizing a chunk of SQL to use left join syntax, the code just needs to add “RIGHT JOIN table” to a statement.

What is difference between drop and delete table?

Delete statement performs conditional based deletion, whereas Drop command deletes entire records in the table. Delete statement removes only the rows in the table and it preserves the table structure as same, and Drop command removes all the data in the table and the table structure.

Why use truncate instead of delete?

TRUNCATE TABLE is faster and uses fewer system resources than DELETE , because DELETE scans the table to generate a count of rows that were affected then delete the rows one by one and records an entry in the database log for each deleted row, while TRUNCATE TABLE just delete all the rows without providing any …

Is truncate faster than delete?

TRUNCATE removes all rows from a table. The operation cannot be rolled back and no triggers will be fired. As such, TRUNCATE is faster and doesn’t use as much undo space as a DELETE.

What do you mean by drop and delete?

DELETE is a Data Manipulation Language command, DML command and is used to remove tuples/records from a relation/table. Whereas DROP is a Data Definition Language, DDL command and is used to remove named elements of schema like relations/table, constraints or entire schema.

What is difference between truncate drop and delete?

DROP statement is a Data Definition Language(DDL) Command which is used to delete existing database objects. Unlike TRUNCATE which only deletes the data of the tables, the DROP command deletes the data of the table as well as removes the entire schema/structure of the table from the database.

What is difference between truncate and delete?

The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log. DELETE command is slower than TRUNCATE command.

What is difference between yank and delete?

To go back to normal mode from any other mode, just press the Esc key. Vim has its own terminology for copying, cutting, and pasting. Copy is called yank ( y ), cut is called delete ( d ), and paste is called put ( p ).

How do you yank multiple lines in vi?

Yank (or cut) and Paste Multiple Lines

  1. Put your cursor on the top line.
  2. Use shift+v to enter visual mode.
  3. Press 2j or press j two times to go down two lines.
  4. (Or use v2j in one swift ninja-move!)
  5. Press y to yank or x to cut.
  6. Move your cursor and use p to paste after the cursor or P to paste before the cursor.

How do you yank in vi?

To yank one line, position the cursor anywhere on the line and type yy . Now move the cursor to the line above where you want the yanked line to be put (copied), and type p . A copy of the yanked line will appear in a new line below the cursor.

What does the indicate in vi?

The “~” symbols are there to indicate end-of-file. You are now in one of vi’s two modes — Command mode. To move from Insert mode to Command mode, press “ESC” (the Escape key). NOTE: If your terminal doesn’t have an ESC key, or the ESC key doesn’t work, use Ctrl-[ instead.

How do I copy text in Vi?

2 Answers

  1. Position the cursor where you want to begin copying.
  2. Press v (or upper case V if you want to cut whole lines).
  3. Move the cursor to the end of what you want to copy.
  4. Press y.
  5. Move to where you would like to paste.
  6. Press P to paste before the cursor, or p to paste after.

How do you use vi?

  1. To enter vi, type: vi filename
  2. To enter insert mode, type: i.
  3. Type in the text: This is easy.
  4. To leave insert mode and return to command mode, press:
  5. In command mode, save changes and exit vi by typing: :wq You are back at the Unix prompt.

How can I edit files without VI?

How to Edit File without vi/vim Editor in Linux?

  1. Using cat as a text editor. Using cat command to create file cat fileName.
  2. Using touch command. You can also create the file using touch command.
  3. using ssh and scp commands.
  4. Using other Programming Language.

What does vi command do in Linux?

vi is an interactive text editor that is display-oriented: the screen of your terminal acts as a window into the file you are editing. Changes you make to the file are reflected in what you see. Using vi you can insert text anywhere in the file very easily. Most of the vi commands move the cursor around in the file.

What are the three modes of VI editor?

While using vi, at any one time you are in one of three modes of operation. These modes are known as “command mode,” “insert mode,” and “last line mode.” When you start up vi, you are in “command mode.” This mode allows you to use certain commands to edit files or to change to other modes.

What are the two modes of Vi?

Two modes of operation in vi are entry mode and command mode. You use entry mode to type text into a file, while command mode is used to type commands that perform specific vi functions. Command mode is the default mode for vi .

What are the vi editor commands?

VI Editing commands

  • i – Insert at cursor (goes into insert mode)
  • a – Write after cursor (goes into insert mode)
  • A – Write at the end of line (goes into insert mode)
  • ESC – Terminate insert mode.
  • u – Undo last change.
  • U – Undo all changes to the entire line.
  • o – Open a new line (goes into insert mode)
  • dd – Delete line.

What are the features of vi editor?

The vi editor has three modes, command mode, insert mode and command line mode.

  • Command mode: letters or sequence of letters interactively command vi.
  • Insert mode: Text is inserted.
  • Command line mode: One enters this mode by typing “:” which puts the command line entry at the foot of the screen.

What was the first text editor?

ed (text editor)

The ed text editor
Original author(s) Ken Thompson
Developer(s) AT Bell Laboratories
Initial release 1973, 47–48 years ago
Operating system Unix, Unix-like, Plan 9

What do you mean by vi editor?

vi (pronounced as distinct letters, /ˌviːˈaɪ/) is a screen-oriented text editor originally created for the Unix operating system. The name “vi” is derived from the shortest unambiguous abbreviation for the ex command visual , which switches the ex line editor to visual mode.

What do you mean by vi editor explain?

visual instrument