1. Filtering
1. Characters and dates should be enclosed in single quotation marks;
2. The keywords of sql are not case-sensitive, but the values in the conditions are case-sensitive;
3. When the date type is converted into a string, the date type also needs to add single quotation marks;
4. Conditional qualifiers are:
| = | equal |
| > | more than the |
| >= | greater or equal to |
| < | less than |
| <= | less than or equal to |
| <>/!= | not equal to |
| := | assign |
| between...and... | between two values (including boundaries) |
| in | |
| like | fuzzy query |
Fuzzy query: %a%: character contains a
%a The last character in the string is a
The first character in a% string is a
The second character in the _a string is a
The third character in the __a string is a
_ means a character
If the query string already contains an underscore (_), the escape character "\" should be used, written as %\_%, or "#" .
is null is empty
is not null
and logical and
or logical or
2. Sorting
order by column asc 正序
order by column desc reverse order
You can also sort by a column first, and then sort by another column, such as: order by column1 asc,column2 desc ;
Attachment: Suggested writing of time clause
In the where clause of the time type: when time is used as a conditional query, it is recommended to write:
where to_char(column_date,'yyyy-mm-dd') between '1998-02-01' and '1998-05-01'
It is not recommended to write:
where column_date between '1-Feb-1998' and '1-May-1998' is not recommended