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71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
# CIS105: Computer Applications & Information Systems Lect. 14
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## Chapter 14: More SQL Statement
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### 14.1: Statement Review
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- `SELECT`: What **fields** (column) you want
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- `fieldname`: If the name is used in only one table
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- `FROM`: What table or tables contain the fields
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- `ORDER BY`: Sorting
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- `DISTINCT`: Use after `SELECT` when you only want to show each vale of the selected field(s) once
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- `LIMIT`: Use when you want to limit the number of records produced
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### 14.2: New SQL Statements
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- `WHERE`: Applies conditions, filters
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- `WHERE` clause conditions follow a pattern: field + comparison operator + value
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- ```sql
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WHERE crime.iucr_no = 420
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```
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- Comparison Operators:
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- `>` : Returns all records larger than the specified value
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- `>=`: Returns all records that are at least as large as the specified value (including the value)
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- `<` : Returns all records smaller than the specified value
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- `<=`: Returns all records that are at least as small as the specified value (including the value)
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- `=` : Returns all records that are exactly equal to the specified value
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- `<>`: Returns all records that are not equal to the specified value
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- `NULL`: An empty value
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- `NOT`: Can be used to create a condition that reverses the logic of any condition
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- Similar logic to the `NOT` function in Excel
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- `AND`: Both conditions must be met for row to be included in query
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- `OR`: Used to combine criteria when we want our results to mach any criteria
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- `BETWEEN`: Shorthand way to include values in a range
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- `IN`: Shorthand way to include values in a range
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- `LIKE`: Use this statement when you aren't sure of the values in a record
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- `%`: any combination of characters
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- `%Keyword`: ends with keyword
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- `%Keyword%`: looks for %keyword% anywhere in the record
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- `Keyword%`: starts with keyword
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- `-` substitutes for any single character
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- '`t_p`' would return '`tip`', '`tap`', or '`top`''; but not '`stop`'
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- '`p_st`" would return '`past`"', but not '`paste`'
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- `'h__s_n'` would return '`hanson`', 'hensen', or '`hansen`'; but not '`harrison`' (note that '`h%s_n`' would return '`harrison`')
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### 14.3: Rules to Remember
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- To combine `AND` and `OR` statements, you must follow the order of operations (`AND` 1st, `OR` 2nd)
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- If `OR` must be first, use `()`
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- All words must be in between `('_')`, `("_")`
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- If your value contains a quotation, use double quotation or a `/`
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- All `#s` is left as-is
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