The difference between count1 and count* in oracle

The key to learning Java without taking detours is: 1. Understand core concepts and grammar; 2. Practice more; 3. Understand memory management and garbage collection; 4. Join online communities; 5. Read other people’s code; 6. Understand common libraries and frameworks; 7. Learn to deal with common mistakes; 8. Make a learning plan and proceed step by step. These methods can help you master Java programming efficiently.

Learning Java requires learning basic syntax, object-oriented programming, collection frameworks, exception handling, multithreading, I/O streaming, JDBC, network programming, and advanced features such as reflection and annotation. 1. The basic syntax includes variables, data types, operators and control flow statements. 2. Object-oriented programming covers classes, objects, inheritance, polymorphism, encapsulation and abstraction. 3. The collection framework involves ArrayList, LinkedList, HashSet, and HashMap. 4. Exception handling ensures program robustness through try-catch block. 5. Multithreaded programming requires understanding of thread life cycle and synchronization. 6. I/O streams are used for data reading, writing and file operations. 7. JDBC is used to interact with databases. 8. Network programming passes S

To connect Oracle database to Tableau for data visualization, you need to follow the following steps: 1. Configure Oracle database connection in Tableau, use ODBC or JDBC drivers; 2. Explore data and create visualizations, such as bar charts, etc.; 3. Optimize SQL queries and indexes to improve performance; 4. Use Oracle's complex data types and functions to implement through custom SQL queries; 5. Create materialized views to improve query speed; 6. Use Tableau's interactive functions such as dashboard for in-depth analysis.

The steps to connect to an Oracle database connection pool using JDBC include: 1) Configure the connection pool, 2) Get the connection from the connection pool, 3) Perform SQL operations, and 4) Close the resources. Use OracleUCP to effectively manage connections and improve performance.

The main reason for integrating Oracle databases with Hadoop is to leverage Oracle's powerful data management and transaction processing capabilities, as well as Hadoop's large-scale data storage and analysis capabilities. The integration methods include: 1. Export data from OracleBigDataConnector to Hadoop; 2. Use ApacheSqoop for data transmission; 3. Read Hadoop data directly through Oracle's external table function; 4. Use OracleGoldenGate to achieve data synchronization.

In Oracle database, the steps to configure parallel query to improve performance include: 1. Set at the database level, and implement it by modifying initialization parameters such as PARALLEL_DEGREE_POLICY and PARALLEL_MAX_SERVERS; 2. Set at the session level, adjust the parallelism of the current session through the ALTERSESSION command; 3. Consider key points such as parallelism, resource management and data distribution; 4. Improve performance by optimizing query planning, adjusting parallelism and monitoring and tuning. These steps help to take full advantage of parallel queries and significantly improve the query performance of the database.

Directly querying administrator passwords is not recommended in terms of security. The security design principle of Oracle database is to avoid storing passwords in plain text. Alternative methods include: 1. Reset the SYS or SYSTEM user password using SQL*Plus; 2. Verify the encrypted password through the DBMS_CRYPTO package.

In Oracle database, if you want to not return the value of a certain field when querying, you can use the following three methods: Only list the required fields in the SELECT statement and do not select the unwanted fields. Create views to simplify queries, but pay attention to the complexity and maintenance costs of the views. Excluding unwanted columns using subqueries or JOINs is suitable for dynamic exclusion of columns, but may affect query performance. Each method has its applicable scenarios and potential disadvantages, and the most suitable method needs to be selected based on specific needs and performance considerations.