Considerations for MySQL migrating Oracle databases

1. Automatic growth of data type processing

MySQL has an automatically growing data type, and the data value is automatically obtained when you insert a record without manipulating this field.

Oracle does not have an automatically growing data type, an automatic growth sequence number is required, and the next value of the serial number is assigned to the field when the record is inserted.

The name of the CREATE SEQUENCE serial number (preferably the table name + serial number tag)

The code is as follows	Copy Code
INCREMENT by 1 START with 1 MAXVALUE 99999 CYCLE NoCache;

The maximum value is determined by the length of the field, and if the defined automatically-growing serial number (6), the maximum is 999999

Insert statement inserts this field value as:

The name of the serial number. Nextval

2. Single quotation mark processing

MySQL can be used in double quotes wrap strings, Oracle can only use single quotes wrap strings. A single quotation mark must be replaced before inserting and modifying a string: Replace all occurrences of one single quote with two single quotes.

3. The processing of the SQL statement page

MySQL processing pages of the SQL statement is relatively simple, with limit start position, record number; PHP can also use seek to locate the result set.

Oracle handles page-flipping SQL statements is cumbersome. Each result set has only one rownum field that indicates its position, and can only be used rownum<100, not rownum>80.

The following are two of the better Oracle page-Flipping SQL statements (field names with IDs as unique keywords):

Statement one:

The code is as follows	Copy Code
SELECT ID, [Field_name,...] From table_name WHERE ID in (Select ID from (select RowNum as Numrow, ID from table_name WHERE condition 1 ORDER BY condition 2) WHERE Numrow > Numrow <) Order BY condition 3;

Statement two:

The code is as follows	Copy Code
SELECT * FROM (select RowNum as Numrow, c.* from (SELECT [Field_name,...] From table_name WHERE condition 1 ORDER BY Condition 2) c) WHERE numrow > Numrow <) Order BY condition 3;

4. Processing of long strings

Processing of long strings Oracle also has its own special place. The maximum operable string length for insert and update is less than 4,000 single-byte, and if you want to insert a longer string, consider using the CLOB type for the field to borrow the Dbms_lob package from Oracle. Be sure to do non-null and length judgments before inserting a change record, and you should warn about field values that are not empty and values that exceed the length field, and return to the last action.

5. Processing of date fields

The MySQL date field is divided into date and time two, and the Oracle Date field is only date, containing the minutes and seconds of the year, with the system time of the current database as Sysdate, to the second, or to the date-type function with a string.

To_date (' 2001-08-01 ', ' yyyy-mm-dd ')

Year-month-day 24 hours: minutes: SEC format yyyy-mm-dd HH24:MI:SS to_date () has a number of date formats, which can be consulted on Oracle DOC.

Convert a Date field to a string function

To_char (' 2001-08-01 ', ' yyyy-mm-dd HH24:MI:SS ')

The mathematical formula for the date field is very different.

MySQL found 7 days from the current time

Date_field_name > Subdate (Now (), INTERVAL 7 day)

Oracle finds 7 days from current time

Date_field_name >SYSDATE-7;

6. Processing of NULL characters

MySQL's Non-empty field also has empty content, Oracle defined a NON-EMPTY field does not allow empty content.

The Oracle table structure is defined according to the NOT null of MySQL, and errors are generated when data is directed. Therefore, to guide the data to judge the null character, if null or empty characters, you need to change it to a space string.

7. Fuzzy Comparison of strings

MySQL with field name like '% string% '

Oracle can also use the field name like '% string ' but this method cannot use the index, the speed is not fast

Using string comparison function InStr (field name, ' string ') >0 will get more accurate search results

8. Procedures and Functions , the operation of the database work, please note that the result set and the release of the pointer.

Edit summary: In MySQL and Oracle migration work we should note that there are 8 points, such as ID, empty characters, fuzzy comparison of strings, related functions in MySQL, time and date processing and single quotes.