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- Usage of nvl in oracle
- The NVL function in Oracle is used to replace values with NULL. The syntax is NVL(value, default_value). Usage includes: checking and replacing NULL with default values; avoiding calculation and aggregation errors; ensuring database integrity.
- Oracle 440 2024-04-30 09:03:15
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- What data objects are there in oracle
- Oracle database data objects include: tables (storage data collections), views (virtual tables), sequences (automatically generate unique values), indexes (speed up retrieval), primary keys (uniquely identify rows), foreign keys (join table data), triggers implements (automatically execute code), stored procedures (encapsulate tasks), functions (return calculated values), and packages (reuse code collections).
- Oracle 476 2024-04-30 09:00:27
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- Usage of substring in oracle
- The SUBSTRING function in Oracle is used to extract specified parts from a string. Syntax: SUBSTRING(string, start, length). Parameters: string - the string to extract the substring; start - the starting position of the substring; length (optional) - the length of the substring. Usage: 1. Specify the starting position and length: such as SUBSTRING('Hello World', 3, 6) returns "llo Wo"; 2. Specify the starting position without specifying the length: such as SUBSTRING('Hello World', 3) Return to "llo Wor
- Oracle 711 2024-04-30 08:57:16
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- How to use decode in oracle
- The DECODE function in Oracle can select a value from multiple values based on conditions. The syntax is: DECODE(expression, value1, result1, value2, result2, ..., default_result). It evaluates an expression against a range of values and returns the corresponding result if there is a match, or a default result if there is no match. DECODE supports nesting, the number of value and result parameters must appear in pairs, and the default_result parameter is optional.
- Oracle 434 2024-04-30 08:54:15
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- How to use connect by in oracle
- CONNECT BY is used to perform hierarchical queries in Oracle. It traverses the data by specifying the hierarchical structure. The specific steps include: creating a hierarchical structure and specifying the connected columns to define the hierarchical structure; setting the connection conditions and using the prior and current keywords to specify the upper structure. The relationship between the first level and the current level, the common condition is prior column_name = current column_name; use advanced functions such as START WITH, CONNECT_BY_ROOT and LEVEL to perform more complex hierarchical queries.
- Oracle 841 2024-04-30 08:51:17
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- The difference between join and left join in oracle
- A JOIN returns only rows that match, whereas a LEFT JOIN retains all rows in the left table, even if there are no matching rows in the right table. JOIN: Joins the left table and the right table, returning only rows with matching rows. LEFT JOIN: Join the left table and the right table, retain all rows in the left table, and fill unmatched rows in the right table with NULL values.
- Oracle 1076 2024-04-30 08:48:14
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- How to write loop statement in oracle
- There are three types of loop statements in Oracle. The syntax is: FOR loop: FOR loop_variable IN [start_value, end_value] LOOP statement(s);END LOOP;WHILE loop: WHILE condition LOOP statement(s);END LOOP;DO WHILE loop: DO statement(s);WHILE condition;END;
- Oracle 709 2024-04-30 08:39:15
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- What does nvl in oracle mean?
- Oracle's NVL function handles NULL values and takes two parameters: an expression and a replacement value. If the expression is NULL, the replacement value is returned, otherwise the expression is returned. Uses include preventing errors, filling null values, and providing consistency.
- Oracle 681 2024-04-30 08:30:26
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- Usage of substr function in oracle
- The substr() function extracts a substring of a string. The syntax is: substr(str, start, [length]). Usage example: Extract the 4 characters starting from the 3rd character from 'Hello World': SELECT substr('Hello World', 3, 4) FROM dual; Result: 'llo'.
- Oracle 794 2024-04-30 08:27:15
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- Usage of if statement in oracle
- The Oracle IF statement is used to execute a block of code based on a condition. The syntax is: IF <condition> THEN <statement> [ELSIF <condition> THEN <statement>] [ELSE <statement>] END IF. It can be used to validate input, perform conditional operations, control loops, and handle exceptions.
- Oracle 1227 2024-04-30 08:24:17
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- How to use where in in oracle
- The WHERE IN clause is used in Oracle to check whether a column value is in a specific value list: Syntax: WHERE column_name IN (value1, value2, ..., valueN) Subquery: WHERE IN subquery can be used to obtain a list of values. Multiple values: WHERE IN checks for multiple values. NULL values: WHERE IN checks for NULL values. Example: Query for departments with id 10, 20, or 30 SELECT * FROM departments WHERE id IN (10, 20, 30)
- Oracle 1055 2024-04-30 08:15:23
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- How to use catsearch in oracle
- CATSEARCH is an Oracle feature for finding string patterns in tables and indexes with the syntax SELECT column_list FROM table_name WHERE CATSEARCH(column_name, search_pattern). CATSEARCH uses regular expressions to define search patterns. Common characters include: . (match any character), * (match the previous character zero or more times), [ ] (match any character within brackets), [^ ] (match within brackets Any character other than), \w (matches word characters), \d (matches numbers). Benefits include: flexibility, performance, ease of use, and
- Oracle 426 2024-04-30 08:12:16
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- How to use grouping in oracle
- The GROUPING function determines the nesting of the grouping level, returning 0 for the outermost grouping and 1 for the inner grouping. Can be used to identify the outermost grouping, calculate aggregate function results, and create conditions based on grouping.
- Oracle 1183 2024-04-30 08:09:15
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- The difference between having and where in oracle
- The difference between HAVING and WHERE clauses is that HAVING is used to filter aggregate results (that is, grouped data), while WHERE is used to filter rows in the base table or view. Additionally, HAVING requires the data to be grouped, while WHERE does not.
- Oracle 683 2024-04-30 08:06:16
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- Can it still be restored after truncate in Oracle?
- Data cannot be restored directly after truncation. Truncation bypasses logging so data cannot be recovered using rollback or flashback queries. To avoid data loss, back up your database regularly and consider truncation operations carefully.
- Oracle 453 2024-04-30 08:00:24
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