1. Relevant knowledge in the database:
1. If the ID is a character value, the following sentence can be used to search for the largest ID value in the database, which is mostly used to manually insert the ID value:
SELECT MAX(CAST(ID AS INT)) AS ID FROM tableName
2. Forced type conversion in SQL statements:
(1) convert (data type, field name), the advantage can format date and value.
(2) cast (field name as data type), easier to use
3. Conversion function in SQL statement
（1）to_char
Example: date to character, to_char (date type field,'yyyy-mm-dd')
Common date pattern symbols:
format symbol Description
yyyy year
mm Display month
dd in numbers in the current month
day day week
am / pm display am / pm
hh / hh12 / hh24 set 12 hour system / 24 hour system
mi minutes
ss seconds
(2) to_number is generally used to convert characters to numeric values
(3) to_date is generally used for character date to date data
2. Escape characters in XML files:
< <less than sign
>> greater than sign
& & and
''single quotes
" "double quotes