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- What does rownum mean in oracle
- The rownum pseudo-column in Oracle returns the row number of the currently selected row, starting from 1 and increasing sequentially. Its usage scenarios include: limiting the number of returned rows, obtaining row numbers, paging, and performing row-level operations. It should be noted that rownum is only applicable to SELECT queries and cannot be updated.
- Oracle 546 2024-05-07 15:18:16
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- The difference between rownum and rowid in oracle
- ROWNUM and ROWID are two different concepts in Oracle: ROWNUM is a pseudo column that returns the row number of the table and is used to limit results or paging queries. ROWID is an internal identifier that uniquely identifies each row in the table and is mainly used for internal data management.
- Oracle 375 2024-05-07 15:09:15
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- What is transaction in oracle
- A transaction is an integral set of logical operations in Oracle Database that either all succeed or all fail. Its properties include atomicity, consistency, isolation, and durability. A transaction consists of data operation statements, transaction control statements and data structures. Its life cycle includes start, execution, commit or rollback. Transactions ensure data integrity, improve performance, handle errors, and simplify the user interface.
- Oracle 1130 2024-05-07 15:03:16
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- What is the function to convert string to date in Oracle?
- The function in Oracle to convert string to date is TO_DATE. The syntax is TO_DATE(string, format_mask), where format_mask specifies the format of the date part in the string. Common formats include YYYY (year), MM (month), DD (date), HH (hour), MI (minute), SS (seconds) and FF (milliseconds). If the string does not conform to the specified format, the function returns NULL.
- Oracle 894 2024-05-07 14:57:16
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- What is the function to convert string to date in Oracle?
- In Oracle, you can convert a string to date format through the TO_DATE function, the syntax is TO_DATE(string_expression, format_mask). format_mask is used to specify the format of the date and time part in the string. Common format mask characters include: YYYY (year), MM (month), DD (day), HH24 (hour), MI (minute) and SS (second) ). For example, the query to convert "2023-03-21 17:30:15" to a date is: SELECT TO_DATE('2023-03-21 17:30:15', 'YYYY
- Oracle 630 2024-05-07 14:54:17
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- How many Chinese characters can be stored in to_char() in Oracle?
- Oracle's TO_CHAR() function can store Chinese characters, the number depends on the character set, character width and data type. In the UTF-8 character set, VARCHAR2 variables can store approximately 1333 Chinese characters, while CLOB variables can store approximately 1.33 million Chinese characters. The amount of storage varies based on character width and content, and Oracle version and configuration also affect capacity.
- Oracle 520 2024-05-07 14:45:27
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- How to use limit in oracle
- The LIMIT clause in Oracle is used to limit the number of rows retrieved. The syntax is: SELECT * FROM table_name LIMIT start_row, row_count. start_row specifies the number of rows to skip (starting from 0), and row_count specifies the number of rows to retrieve.
- Oracle 964 2024-05-07 14:42:14
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- How to intercept string in oracle
- There are three ways to intercept strings in Oracle: SUBSTR function: extract substrings based on starting position and length. INSTR function: Determine the position where the substring appears, and intercept the string with the SUBSTR function. REGEXP_SUBSTR function: Extract substrings from strings using regular expressions.
- Oracle 825 2024-05-07 14:39:18
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- explain usage in oracle
- EXPLAIN is used in Oracle to analyze the execution plan of a SQL statement to help the optimizer choose the best path. By adding EXPLAIN PLAN FOR before the SELECT statement, you can obtain a text report containing information about the execution path, operation type, cost, predicates, etc. When analyzing a plan, paths are identified, costs are checked, predicates are analyzed, indexes are considered, and actions are taken based on the output to optimize performance, such as creating indexes or rewriting queries.
- Oracle 838 2024-05-07 14:33:18
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- What is the difference between double quotes and single quotes in Oracle
- In Oracle Database, double quotes quote object identifiers (such as table names), and single quotes define string literals. Single quotes in single-quoted strings need to be escaped, are case-sensitive, and cannot be spliced; double-quoted strings are not case-sensitive and can be spliced.
- Oracle 617 2024-05-07 14:30:24
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- What is the difference between double quotes and single quotes in Oracle
- Double quotes and single quotes are used to surround string values in Oracle. The main differences are: Purpose: Single quotes are used for string literals, while double quotes are used for database object names, single-quoted literals, and case-sensitive identifiers. Identifier naming: case-insensitive within single quotes, case-sensitive within double quotes. Escape characters: The escape characters must be escaped with backslashes within single quotes, but they do not need to be escaped within double quotes.
- Oracle 552 2024-05-07 14:24:34
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- What is the difference between single quotes and double quotes in Oracle
- In Oracle, single quotes are mainly used to define string values and identifiers, while double quotes provide functions such as escape character processing, identifier conflict resolution, and string concatenation: Escape character processing: Double quotes allow the use of escape characters, Single quotes cannot. Identifiers: Single quotes are used for object names, double quotes are used for object names that conflict with keywords. String concatenation: Double quotes concatenate strings and the escaped characters they contain, while single quotes only concatenate the string value itself. Comments: Double quotes can be used for inline comments, but single quotes cannot.
- Oracle 389 2024-05-07 14:18:18
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- How to express not equal to empty in Oracle
- The syntax for not equal to null in Oracle is IS NOT NULL. This operator checks whether a column or variable contains data; values that contain no data or contain an empty string are treated as NULL. Use the IS NOT NULL operator to filter the result set or to ensure that a column or variable is not NULL before inserting or updating.
- Oracle 1109 2024-05-07 14:12:14
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- How to write not equal in Oracle
- The operator used to express inequality in Oracle is "!==", which compares two values and returns a boolean value of whether they are not equal. The syntax is: expression1 != expression2. This operator can also be expressed as "<>" and is used to filter unequal values.
- Oracle 817 2024-05-07 14:09:15
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- How to express equal in oracle
- In Oracle, the equal sign is represented by a double equal sign (==) and is used to compare expression values. If they are equal, True is returned, otherwise False is returned.
- Oracle 289 2024-05-07 14:06:12
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