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1. Error message
When using PL / SQL to connect to Oracle, the error message is as follows: 
The reason for this error is: Install PL / SQL on a 64-bit operating system. PL / SQL only supports 32-bit operating systems. The solution is to load an additional oci.dll file.
2. Solution
Download PL / SQL green package: https://pan.baidu.com/s/1XlyLIsNMVVHLqKAXwOJyUg extraction code: qhwm Download client: https://pan.baidu.com/s/1FZClDR9_fi7i72lG2NFEbw extraction code: 1c5g
After the download is complete, unzip the PL / SQL green package and the client, and specify the Oracle home directory and the OCI library directory in PL / SQL (here the uncompressed client is placed directly under the root directory of the c drive)
After configuring the above information, remember to configure the tnsnames.ora file in the client directory 